That size tank really limits your options to a few suitable species. Too small for Malawi mbuna, but Tanganykian shelldwellers would work. Multi's are the smallest cichlid in the world, and a trio of those and a pile of shells would go well in one end of the tank. A rockpile at the other end would work with a few J. transcriptus, and you could also fit a single Calvus in the mix.
Brichardi or any of their close relatives are suitable for a species tank. They breed quite prolifically, and as the fry grow their territory expands. Any other fish will be stressed to death if not killed outright, and the overcrowding as multiple broods of fry grow out will create a mess.
The demasoni are fine in large numbers (12-15) but that's too many for your tank size. A half-dozen will eventually end up as one that has killed the rest. Set up a larger tank and add a half-dozen yellow Lab's with the demasoni, and you'll have a very colorful and active tank full of fish. For that matter, I have a used 90 gallon setup (black tank, pine stand w/matching canopy, glass tops) available for $160. Also have an older (thicker glass, no center brace) 75 tank and glass top for $80.
Your tank dimensions arent really suited to malawi as you want the length not the height. Tanganikan cichlids will be better suited.
