32" by 12" footprint. Are you aiming for breeding? If so I'd stick to one species and try 1m 2f (or even 1m 1f). I might be tempted to go for 2 pairs of different species in a 36" but would be worried about what would happen if and when breeding happened and I had something similar planned for a 48".
If you're not going for breeding then go for males of different species, and yes, I'd expect you could probably get 2 that looked different enough from each other (you could go for females if you were so inclined, but they're a lot less pretty).
As usual, it depends on the temperament of the individual fish. I have a male agassizi at the moment that's an absolute psychopath, I'd not keep him with anything that looks remotely like him (he even attacks the cat through the glass), but that's just the way it goes.
Only other question I have is whether they're going to be the only things in the tank or if it's planned to be a community.