In my opinion it seems fine as is, the rule of thumb is 1 inch of fish to 1 gallon of water, but its always more complicated, you also don't want to overstock levels of your tank as well. 55 gal
is a big tank, as of right now it seems like for your bottom feeder/ low level you 14 fish 1in -2in, for you Shoalling/Mid level you have 12 fish all about 2in -2.5in, and your Top level your dwarf Gourami about 3in probably and most likely enjoys its own space. Snails and other invers I usually don't count unless you have a ton of them.
All in all I'd say if you want a few more it'd be fine, stay away from more bottom level fish like Pleco's/Rainbow Sharks/Cory's as you have the most of those. The amount depends on the size, if you want something big like Gourami's id keep it to 2-3, something shcoalling size like mollies or tetras 3-5.