I looked into getting one of these for a while, too (though I never followed through on it as I do not have the right accomodations). African butterfly fish prefer warm acidic water. As they spend a lot of time at the water's surface, it helps to have some floating plants present and a relatively slow current. They are carnivores and prefer live insects like crickets. They do fine with peaceful mid-level and bottom-dwelling species, but are sometimes known to nip at other top-dwelling species unless the tank is large enough for the fish to have their own areas of the tank. It's best not to put them with fin-nippers like barbs, either, as the african butterflyfish is not a fast swimmer and has long, flowing fins.
They're truly beautiful fish, and can be kept in a relatively small tank. Best of luck keeping them!