What size is your tank?
Essentially that is the biggest limiting factor of what you can keep.
As for the aggressive cichlids from what I have read you can either keep one (or a pair), or keep them in a larger group to spread the aggression finely, but that requires a very large tank.
I keep Jack dempsey, oscar, and jag in my big tank as cichlids, with other fish to help distract them from each other.