Firemouth usually do well in a community semi aggressive setup, If kept alone. If they begin to breed, issues shall arise. I have a single firemouth in with fish half his size and he doesn't bother them much. He really mellowed out when I put a male sajica in there despite being much smaller. I would try and find a blue eyed sajica they are lovely and stay smaller. A pair of rainbow cichlids, festivums, some of the smaller geophagus would be nice. Pictus catfish are hilarious. It my end up being crowded in the future but as it usually goes you WILL GET A BIGGER TANK.