catfish

I have a royal pleco catfish. He is lying with his mouth up. We have asked our local shop and they said to keep him in the dark and give him some food. Is there anything else we can do. Any help will be thanked

TL;DR- will fishies of the same species but different breed still school and be happy? How many is overcrowding in 10 gal heavily planted + 2 mystery snails? (New to fish) Adding fish to my 10 gal heavily planted aquarium with two very happy mystery snails and a large and medium rock formation...

So I'm getting a free 55 gallon tank from a friend and I'm super excited about it. However, I don't really know what kind of fish I want to fill it with. I want freshwater, something other than chiclids, something with personality, maybe something not too hard too keep but at the same time not...