For larger tanks, I love seeing bala sharks, active, and will school/shoal. The pictus cats will be active and all over, but would snack on swordtails, both adults and juveniles. Perhaps some other synondontis cats instead. Someone suggested rainbows, these are great, my favorite are the Madagascar rainbows. Another suggestion would be red line or denison barbs, striking larger fish.
I have had good fortune with oscars, raising them with other Central Americans , and have never had an issue with a feisty Oscar, but others have learned otherwise. But going with oscars and other large fish means nothing like the pictus cats, swordtails, or rainbows.
Perhaps with the firemouths, add in a salvini cichlids. In my Central American tank, I had a school of giant danios, that a
Ways schooled because of the predatory fish. The key is a predator who is not quite big enough to get the danios.
I always think bichirs are cool. Bichir, tiger shovelnose, a nice pleco of some variety with nice markings, silver arrowana, with bala sharks to swim all over, and you have a cool display.