Your current plan does leave room for some more fish - nothing big or high waste, but a couple of small loaches wouldn’t hurt.
I’ll see if I can find the source later but there was someone with dojo loaches that were close to 15 inches long. They were in a 300 gallon planted tank I think, with a bunch of danios and rosy barbs and panda cories. Was a cool cold water community tank. (No pun intended)only weather loaches can be kept alone, but they get up to 20 inches in wild and 12 inches in home aquariums, so they can't live in a 55 gallon tank. All other loaches need to kept in groups
I'm sure you'll get plenty of good ideas here, but I just thought I'd note that you can keep exodons with other fish. No doubt there's some risk, and it'll depend on the type of fish, but I've got 20 exodons with a bristlenose pleco and three corys, and the exodons completely ignore them. This tank has been stable like this for months, getting close to a year now. I've seen clown loaches with exodons, too, though I haven't tried that myself.Ok, what unusual schooling fish are there? Like tetras, barbs, etc.
I'm not interested in Exodons as I want to have other fish in the tank, and I'm not going to put them at risk with little piranhas, but I'm now open shop for other types of tetras.
Ok so how does this setup sound: 1 Senegal Bichir, 1 Striped Raphael Catfish, 1 Syno species Cat (preferably a featherfin if I can find one), 2-3 Electric Blue Acaras OR 2-3 Geophagus TapahoPlenty of options involving a senegal bichir. Due to being a smaller bichir, there are a lot of fish that don’t fit in their mouths.
Medium sized cichlids would be good, as well as some sort of schooling fish (you need some activity in there). African butterfly fish are good with them. The raph would be fine.
I wouldn’t do loaches with one though - if the bichir tries to eat them the spines could be an issue.