^ maybe, but would be a bit cramped for a 20 IMO. I'd go with something like:
8 neon tetra
6-8 of another schooling fish like rummynose tetra or harlequin rasbora (many other options here)
1 dwarf gourami (don't get any of the larger gourami types)
6 small corys, like panda, pygmy or dwarf (they prefer sand, but if your gravel is rounded and smooth it should be ok. If it's sharp, it isn't)