con...if you want you could do a pair and some dithers but I wouldn't go much more than that because as they get larger and reach full size they'll want the whole tank as their territory..if they're breeding that is
blood parrot...imo they'll get too big for that size tank...they can get to 8" or more and are very bulky, imo best for a 75 minimum
any vieja...pretty much any Vieja/Paratheraps is going to grow too large for anything smaller than a 75 gallon
geos....some Gymnogeos stay small enough for your tank. G. balzanii are nice but they may not be the easiest to find.
honduran red point(hrp)....very nice and a couple of pairs would probably be fine in that size tank. the only problem is it may be difficult to find TRUE HRP's and not HRP x Cons which are often sold as HRP's or simply as blue cons at LFS
firemouth...IMO, this would be the best way to go...I'd get 6 juveniles and a top-dwelling schooling/shoaling fish and set up a nice display tank. platys would probably work perfectly with them as they are found in the same areas in the wild with firemouths anyway, plus when the platys start to breed, the fry will make a nice snack for the firemouths.
thomas/butterfly cichlid[?]...I assume you're talking about the african butterfly cichlid? if so I don't know much of anything about them so someone else will have to chime in here
salvini...a pair would possibly work though I have heard of males growing fairly large..in the 8" range and not sure how much conspecific aggression you'd see between a pair in that size tank though overall I think they'd probably be ok
severum[?]...imo, severums should be kept in 75 gallon minimum. I know a lot of sites say they only grow 6" but I've seen them in the 8-10" range and they're incredibly bulky so a 75 gallon really would be much better for them
