Iv'e just been hearing south americans. Have you considered african cichlids? The Mbumbas to be exact. From lake Malawi. Very Active fish and you can acquire quite a variety at your lfs. As for quantity, you could have quite a few in there. But if your wanting to stick with the south american's you could definately do a jd or two. Or even the ebjd, their beautiful fish. They are a little expensive if your just starting out, but theyre no harder than any of the others listed.