Darters are relatively easy to keep and many of them will quickly acclimate to flake food so you shouldn't have much trouble keeping them alive. Frozen 'water fleas' (Daphnia) are usually available in a well-stocked local fish store and will likely be much appreciated as will frozen 'bloodworms'. They are not truly 'tropical' fish (or they wouldn't be native to North America) but since yours likely came from somewhere in Florida I wouldn't subject them to excessively cold water. They will probably be fine in an aquarium at room temperature or slightly warmer. Most darters (but not all) prefer fairly fast-moving water so a decent current (provided by your filter) will probably be appreciated. They are generally not aggressive toward other fish, though the males can be rather rough with each other during breeding season. Obviously you don't want to keep them with other fish that might consider them a snack.
-Joe