Can i put 4 gouramis, 10zebra dianos,6 molly's in a 55gal?

Yes they should be okay together if the tank has been cycled. Well the danios would probably do fine to cycle the tank as they are quite hardy, but wait in the other until after cycling. I assume you have a filter and heater and all that good stuff too. I would put some decorations in the tank, like some fake plants and rock or driftwood. You can make the tank look nice to you as long as the fish have some cover to feel secure, they will be fine. Castles and priates ships work too if that is your style. As for catfish, I would use corydora catfish but get a group of five or more so they can school. Most other species of catfish get large and will eat small fish. For food, tropical flakes should be fine for everyone but you should get some sinking food for the catfish when you get them.