Here is a description (done by me) of the 24 extant species of Crocodilian (there may be 25 but I chose not to include Crocodylus raninus). Note that ranges are based off of their NATIVE ranges - there are a few populations of a few species outside of their native ranges, those aren't being counted though. Also, populations listed under the conservation section are wild adults, no captive populations are accounted for in this. Finally, average sizes listed are for mature adults False Gharial, Tomistoma schlegelii Size: averages 10-12 feet in length, largest recorded was 16 feet and could potentially reach 20 feet Range: found in Malaysia and Indonesia Conservation: listed as vulnerable by the IUCN, estimated to be less than 2,500 adults left Diet: primarily fish, but won't hesitate to eat monkeys, deer, water birds, or other reptiles Captive Care: this large species should have an enclosure at least 650 square feet, with at least 250 square feet of haul-out space, and a pool at least 6 feet deep Gharial, Gavialis gangeticus Size: averages 10-15 feet in length, largest recorded was 20 feet and could potentially reach 24 feet Range: found in India, Myanmar, and Pakistan Conservation: listed as critically endangered by the IUCN, estimated to be less than 250 adults left Diet: almost entirely fish, although crabs make their way into the diet as well Captive Care: this is a large species that needs an enclosure of around 800 square feet, with at least 300 square feet of haul-out space, and a pool at least 8 feet deep Broad-Snouted Caiman, Caiman latirostris Size: averages 6-8 feet in length, largest recorded was 11 feet Range: found in Brazil, Uruguay, Paraguay, Bolivia, and Argentina Conservation: listed as least concern by the IUCN Diet: consumes a varied diet consisting of various fish, snails, reptiles (including turtles), and birds Captive Care: being a smaller species, they can be successfully housed in an enclosure of 360 square feet, with at least 135 square feet of haul-out space, and a pool at least 3 or 4 feet deep Yacare Caiman, Caiman yacare Size: averages 6-8 feet in length, largest recorded was 10 feet and could potentially reach 13 feet Range: found in Brazil, Paraguay, Bolivia, and Argentina Conservation: listed as least concern by the IUCN, and there are over 10,000,000 of them in Brazil alone Diet: mostly piranha-sized fish, along with reptiles, birds, and smaller mammals - larger caimans will take down peccaries and capybaras Captive Care: being a smaller species, they can be successfully housed in an enclosure of 360 square feet, with at least 135 square feet of haul-out space, and a pool at least 3 or 4 feet deep Spectacled Caiman, Caiman crocodilus Size: averages 4-6 feet in length, largest recorded was 8 feet and could potentially reach 10 feet Range: found in Mexico, all of Central America, Colombia, Venezuela, Guyana, Suriname, French Guiana, Ecuador, Peru, Bolivia, and Brazil Conservation: listed as least concern by the IUCN Diet: mostly fish and snails, with larger caimans eating larger mammals like peccaries and capybara Captive Care: this is a small species, and can be housed in an enclosure of 260 square feet, with at least 100 square feet of haul-out space and a pool at least 3 feet deep Black Caiman, Melanosuchus niger Size: averages 9-12 feet in length, largest recorded was 16 feet and could potentially reach 20 feet Range: found in Brazil, Peru, Bolivia, Colombia, Guyana, Suriname, and French Guiana Conservation: listed as conservation dependent by the IUCN Diet: larger fish, snakes, turtles, birds, and mammals such as capybara and peccaries - even jaguars and river dolphins have been known to be eaten by large caimans Captive Care: these are large crocodilians, and need an enclosure that's at least 525 square feet, with at least 200 square feet of haul-out space and a pool at least 5 feet deep Smooth-Fronted Caiman, Paleosuchus trigonatus Size: averages 4-6 feet in length, largest recorded was 8 feet Range: found in Brazil, Bolivia, Peru, Ecuador, Venezuela, Colombia, Guyana, Suriname, and French Guiana Conservation: listed as least concern by the IUCN Diet: mostly terrestrial animals such as lizards, snakes, birds, and small mammals - and only occasionally eats fish or snails Captive Care: this isn't a particularly large caiman, and can be kept in an enclosure of 260 square feet, with at least 100 square feet of haul-out space and a pool at least 3 feet deep Cuvier's Dwarf Caiman, Paleosuchus palpebrosus Size: averages 4-5 feet in length, largest recorded was 6 feet and could potentially reach 7 feet Range: found in Brazil, Paraguay, Bolivia, Peru, Ecuador, Colombia, Venezuela, Guyana, Suriname, and French Guiana Conservation: listed as least concern by the IUCN Diet: consumes a varies diet consisting of fish, amphibians, small mammals, birds, crabs, and terrestrial invertebrates Captive Care: being the smallest of the caimans, they only need an enclosure of 200 square feet, with at least 75 square feet of haul-out space and a pool at least 2 feet deep Chinese Alligator, Alligator sinensis Size: averages 4-5 feet in length, largest recorded was 7 feet and could potentially reach 10 feet Range: found only in far eastern China Conservation: listed as critically endangered by the IUCN, with less than an estimated 150 adults left Diet: mostly clams, snails, insects, and fish - larger specimens will eat birds and small mammals with more frequency Captive Care: while not a massive species, they should still have at least 320 square feet of enclosure space, with at least 120 square feet of haul-out space and a pool at least 3 feet deep American Alligator, Alligator mississippiensis Size: averages 8-10 feet in length, largest recorded was 17 feet and could potentially reach 20 feet Range: found in the United States, namely North and South Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, Arkansas, Texas, and Oklahoma Conservation: listed as least concern by the IUCN Diet: very generalist diet, consuming prey such as larger fish, water birds, turtles, bullfrogs, snakes, muskrats, and raccoons - larger alligators will eat animals like deer and wild boar as well Captive Care: these animals can grow quite large, so a 550 square foot enclosure with at least 200 square feet of haul-out space and a pool at least 5 feet deep should be considered the minimum size Dwarf Crocodile, Osteolaemus tetraspis Size: averages 4-5 feet in length, largest recorded was 6 feet Range: found in countries along the Ivory Coast of Africa, from Guinea and Sierra Leone west to Nigeria and Cameroon, then south to Angola and Dem. Republic of the Congo - also found in Mali, Niger, Central African Republic, and Chad Conservation: listed as vulnerable by the IUCN Diet: mostly fish and larger aquatic invertebrates, and occasionally carrion during the dry season Captive Care: being a smaller species of crocodile, the minimum enclosure size considered should be 200 square feet, with at least 75 square feet haul-out space and a pool at least 2 feet deep American Crocodile, Crocodylus acutus Size: averages 8-12 feet in length, largest recorded was 18 feet and could potentially reach 22 feet Range: found in Florida, Mexico, all of Central America, Venezuela, Colombia, Ecuador, Peru, and most of the Caribbean Conservation: listed as vulnerable by the IUCN Diet: some of the most opportunistic crocodiles, their diet is known to consist of fish (freshwater and saltwater), crabs, water birds, turtles (including sea turtles), snakes, possums, raccoons, dogs, peccaries, and livestock such as goats, pigs, and cattle Captive Care: these are large crocodiles, meaning the minimum enclosure size considered should be 700 square feet, with at least 260 square feet of haul-out space and a pool 6 or 7 feet deep Orinoco Crocodile, Crocodylus intermedius Size: averages 10-14 feet in length, largest recorded was 17 feet and could potentially reach 22 feet Range: found in Colombia, Venezuela, Guyana, and Brazil Conservation: listed as critically endangered by the IUCN, with anywhere between 250-1,500 adults left Diet: primarily fish, although turtles, water birds, capybara, and smaller livestock are all fair game Captive Care: these are large crocodiles, meaning the minimum enclosure size considered should be 700 square feet, with at least 260 square feet of haul-out space and a pool 6 or 7 feet deep Freshwater Crocodile, Crocodylus johnsoni Size: averages 7-10 feet in length, largest recorded was 13 feet Range: found only in northern Australia Conservation: listed as least concern by the IUCN Diet: mostly fish, but also water birds, bats, large frogs, turtles, and snakes - larger crocodiles may eat prey the size of wallabies Captive Care: for crocodiles these species are rather small, meaning that they can be kept in an enclosure of 320 square feet, provided it has at least 120 square feet of haul-out space and a pool at least 3 feet deep Philippine Crocodile, Crocodylus mindorensis Size: averages 4-6 feet in length, largest recorded was 10 feet Range: found only in the northern Philippines Conservation: listed as critically endangered by the IUCN, somewhere around 100 adults are presumed to be left Diet: opportunistic hunters, eating fish, snails, shrimp, small mammals, birds, and snakes Captive Care: for crocodiles these species are rather small, meaning that they can be kept in an enclosure of 320 square feet, provided it has at least 120 square feet of haul-out space and a pool at least 3 feet deep Morelet's Crocodile, Crocodylus moreletii Size: averages 7-10 feet, largest recorded was 15 feet Range: found in Mexico, Belize, and Guatemala Conservation: listed as least concern by the IUCN Diet: not much of a fish eater, they often eat small mammals, birds, and reptiles - larger crocodiles will eat larger mammals like tapir and cattle Captive Care: for crocodiles these species are rather small, meaning that they can be kept in an enclosure of 320 square feet, provided it has at least 120 square feet of haul-out space and a pool at least 3 feet deep Nile Crocodile, Crocodylus niloticus Size: averages 10-12 feet in length, largest recorded was 21 feet and could potentially reach 26 feet Range: found nearly everywhere in Africa except for the northern part, including Madagascar Conservation: listed as least concern by the IUCN Diet: lots of large fish, but also water birds, other crocodiles, mammals ranging in size from jackals to hippos, and carrion Captive Care: these are large crocodiles, and the minimum enclosure size should be 675 square feet, with at least 250 square feet of haul-out space and a pool at least 6 feet deep New Guinea Crocodile, Crocodylus novaeguineae Size: averages 5-8 feet in length, largest recorded was 11 feet Range: found only in New Guinea Conservation: listed as least concern by the IUCN, with a population of 50,000 to 100,000 adults Diet: mostly fish, but also consumed shrimp, crabs, frogs, snakes, birds, and bats Captive Care: being a smaller crocodile, they only need 260 square feet of enclosure space, provided that 100 square feet of it is a haul-out and there is a pool at least 2 or 3 feet deep Mugger Crocodile, Crocodylus palustris Size: averages 8-10 feet in length, largest recorded was 12 feet and could potentially reach 16 feet Range: found in India, Pakistan, Sri Lanka, Nepal, Bangladesh, and Myanmar Conservation: listed as vulnerable by the IUCN Diet: these are opportunistic predators that eat fish, snakes, turtles, water birds, monkeys, squirrels, and otters - larger crocodiles are known to eat deer and buffalo Captive Care: these are large crocodilians, and need an enclosure that's at least 525 square feet, with at least 200 square feet of haul-out space and a pool at least 5 feet deep Cuban Crocodile, Crocodylus rhombifer Size: averages 6-8 feet in length, largest recorded was 11 feet Range: found only in a small part of Central Cuba Conservation: listed as critically endangered by the IUCN Diet: mostly small mammals like hutia (guinea pig-like animals) and rats, as well as fish and turtles Captive Care: being a smaller species, they can be successfully housed in an enclosure of 360 square feet, with at least 135 square feet of haul-out space, and a pool at least 3 or 4 feet deep Siamese Crocodile, Crocodylus siamensis Size: averages 4-7 feet in length, largest recorded was 13 feet Range: found in Indonesia, Malaysia, Thailand, Vietnam, and Cambodia Conservation: listed as critically endangered by the IUCN Diet: mostly fish, as well as snakes, larger frogs, and small mammals Captive Care: these crocodiles need at least 420 square feet of enclosure space, of which 160 square feet must be dry land and the pool must be at least 4 feet deep West African Crocodile, Crocodylus suchus Size: unknown [please let me know if you have information to fill in this space] Range: found in pretty much all of Central Africa Conservation: unknown [please let me know if you have information to fill in this space] Diet: unknown [please let me know if you have information to fill in this space] Captive Care: unknown [need to know the average size to develop care recommendations] Saltwater Crocodile, Crocodylus porosus Size: averages 10-16 feet in length, largest recorded was 20 feet and could potentially reach 33 feet Range: found in India, Sri Lanka, Bangladesh, Myanmar, Thailand, Cambodia, Vietnam, Malaysia, Indonesia, the Philippines, New Guinea, and Australia Conservation: listed as least concern by the IUCN Diet: mostly fish eaters, but they also commonly consume other crocodiles, water birds, and mammals the size of dingoes or kangaroos - the largest crocodiles eat animals like buffalo and livestock Captive Care: A 640 square foot enclosure should be the smallest size that these large crocodiles are kept in, with at least 240 square feet of dry land and a pool at least 6 feet deep Slender-Snouted Crocodile, Mecistops cataphractus Size: averages 5-8 feet in length, largest recorded was 14 feet Range: found throughout most of Central Africa Conservation: listed as critically endangered by the IUCN, with anywhere between 1,000 and 20,000 estimated to be around today Diet: pretty mush solely aquatic prey, such as fish, crabs, and frogs - although they sometimes eat small mammals, snakes, water birds, and turtles Captive Care: these are moderately-sized crocodiles, and they should be housed in an enclosure at least 450 square feet - with at least 170 square feet of haul-out space and a pool at least 4 feet deep
Some of the leading authorities on captive keeping of crocodilians summarized minimum enclosure size (water+land) and water depth in an article a few years ago (note: minimum). It's in German, but the table in the last part of the article is easy enough to decipher even if you don't understand that language. http://www.kroko-treff.de/agkrokodile_neu/docs/Mindestanforderungen_Krokodile.pdf As mentioned in the article text, strict enclosure area can be a bit misleading, as it depends as much on having an enclosure that is shaped in a way where individuals can get out of the line-of-sight of each other (e.g., roughly "C"- or "S"-shaped when seen from above). The West African crocodile is, as suggested by its name, primarily West African, although it extends well into Central Africa where it meets the Nile croc. West African generally reach a maximum size of 2.5-3 m (8-10 ft), with most individuals even smaller, and combined with the medium aggressive behavior they really are a very different "beast" than the larger and often quite aggressive Nile. Similar-sized Crocodylus in the above pdf is a good guideline for minimum enclosure that would suit a West African, too. With a few minor tweaks, all Crocodylus (incl. West African) have similar feeding ecology, which basically means that smaller species and individuals take fish and whatever medium-small animal they can catch, while large individuals of the large species will try almost anything. Although some marginal populations of the West African likely are seriously threatened (e.g., the famous desert populations), extrapolated locality data indicates that it overall is both widespread and at least locally fairly common. On that basis it is likely that the West African is Least Concern or at most Vulnerable. It is perhaps worth mentioning that population number you provide are wild only. For example, there are literally thousands of captive Chinese alligators and hundreds of gharials.
I'd be interested to know whether you have any source for your cited captive care requirements, or merely guessed at suitable dimensions - several of the proposals sound a little too small to me. Also, although you nod towards the potential existence of Crocodylus raininus, your total number of taxa is incorrect given the fact that both the Dwarf Crocodile and Slender-snouted Crocodile have been split; the latter is pretty conclusively two species, whilst the former is still under some debate but is certainly more than one species.
@TLD, to make it even more messy an interesting split seems to have occurred with American crocs and Cubans, with Meso-American Amercians aligning in one sub-population and Americans from the Caribbean and notably also Cuba very close to Cubans, but not quite! This seems to make a case for that American crocs might also be 2 separate taxa.
