I'm sorry to say but you have a lot of potentially big fish
Rainbow Sharks- 6 inch (ok, though should only really have one, or 6 or more)
Red Tail Sharks- 7 -8 inches (Ok but as above, isn't compatible with rainbows, pick one species and stick with it)
Black Sharks- 20+ inch ( Oooh boy, you might want to rehome these guys, unless you upgrade to a massive tank...)
Bala Sharks- 14 inch (Needs a school of 6, and theres no way you can fit that big a school in a 55, extremely skittish when housed alone, often injuring itself from getting scared and banging into things)
Dwarf Gourami- 2 inch (It's fine in your tank, but not compatible with other gourami, and may be lunch to the sevs)
Blue gourami- 6 inch (ok, but as above not compatible, probably wont go well with the sevs either)
Angel fish - 6 inch (could be ok, not sure on compatibility between it and Severums)
Severums- 10-12 inch ( ok, but you can only keep one, you could keep two if there were no other fish in the tank)
Plecos- depending on species these guys can get anywhere between 6 inch and two feet, if their commons they'll grow massive, if their bristlenoses their fine, dont really no much about these guys.
I'd advise cutting down to
1 shark (red tailed or rainbow, these guys are fantastic scavengers)
2 Severums
You'd need to keep on top of water changes, but that could work.
Or you could keep the Angel fish, a shark and perhaps the gouramis, not sure on compatibility.
Hope that helps
Emma