The t-bar is fairly similar in aggression to the firemouth. The problem is that all these moderately territorial fish can't definitively be combined in quantity inside that space. It may not work even if their temperaments are similar. The more aggressive fish get, the more space they need. If you want to maximize the amount of fish you can stick in your aquarium than shifting to more peaceful fish is the way to go. That being said, the reality is with fish on these aggression levels in the amount that you seem to want to stock them the only thing you can really do is try it. Just be prepared to remove fish if it becomes problematic.
