A standard 20 gallon aquarium should be fine for four leucomelas or auratus. If you're buying juveniles you might consider raising them in a smaller enclosure until they are five or six months old and then moving them into the larger tanks.
I'd recomend feeding a varied diet of both crickets, flies and any other small feeders that you have access too. Drosophila can make up the majority of the frog's diet, but if you're able to toss crickets in every few feedings that would be ideal. Other food items to look into are springtails, termites and rice flower beetles, all of which aren't necessary but are nice to feed occasionally.
The most important thing is that you start out with healthy frogs. At the show you will be able to inspect the frogs yourself to insure that they are in good health. You probably won't be able to find the frogs much cheaper than the prices you listed, but you will be able to look them over before you buy them. If these are your first dart frogs it might be even better to just buy from a respected breeder with a good reputation such as Patrick Nabors of www.saurian.net or Sean Stewart of www.herpetologic.net that way you can be sure you are starting with healthy animals. Good luck,
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Devin Edmonds
devin@amphibiancare.com
www.amphibiancare.com
