Tinfoil barbs get too big for a 55. Even one would be miserable in there.
I'd do a Bristle-nose pleco. They stay small, eat algae and are little clowns all around. Or a small school of the same species[i/] of cories.
Angelfish are a great choice for the average 55 tall. I'd not try keeping more than seven at the most, not because of stocking but for territories. Most angelfish are little bicker-wasps about space. I'd personally stay under five, but success varies with the individuals involved.
The gouramies are a great idea. Stick with Trichogaster species and only get maybe two or three, as they will annoy the Angels.
As far as large Cyprinid "Sharks" are concerned, avoid black sharks (too big). There are two common red-and-black sharks. One is known to be aggressive and the other downright friendly, so do that search. And no Balas. They need to be in schools, usually, and each get a foot long. So to keep five balas you would need around 100 gallons minimum, as they like to roam. The inch-per-gallon rule here is way wrong for most of the fish you are interested in, so forget about that yardstick. Plecos are waste machines, cories aren't as bad. Angels can be fed lightly but have vertical mass to consider.
This is a great assortment and I'm sure whatever you choose will make you happy. Enjoy.
The angels and cories like higher temps (82º+) but I believe Trichogaster are a bit cooler. They can get air from the surface, too, but to avoid metabolism issues, I'd keep a tank of these species at around eighty.
I almost forgot! If you like the shark look, look into Botias!
