Ropefish are fun in a 55 gallon. They're not aggressive but will eat any fish that easily fit in its mouth (neons and danios). I just have to recommend them cause they're my personal favorite lol.
When I think about stocking a tank, I first pick the type, which it seems you want to go with community fish. So next I would think of the three levels of a tank.
•Think about a bottom cleanup crew when stocking, I highly recommend Siamese Algae eaters, but there's also snails, Cory cats, shrimp, etc
•Think about your "show fish" or "main attraction" it can either be a single eye catching fish, or a flashy school of fish. Generally fish that swims in the middle level of the aquarium.
•Then you can add a couple top swimmers such as hatchets or an African butterfly.
As for how many fish and so forth, check aqadvisor.com as mentioned in a previous comment.
Good luck and happy fishing