I'm also a gnube, but I'm 1 month into my 20 gallon long, so I think I can maybe share my experience -- like a sci-fi movie where you go back in time 1 month to tell former-you about the future

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My 20 has 1 dwarf gourami, 8 zebra danios, 8 julii corys, and a few apple snails. It's planted with sand substrate and an AquaClear 50 HOB filter.
Everyone seems to be getting along fine, so I think my overall scheme is good. If your 20 is a HIGH and not a long, then I wouldn't recommend danios -- they like space to zip and zoom. They're very active, which is fun to watch. The corys aren't as active as I hoped -- mostly sit under the wood and plants, but they are pretty cute when they're sifting through the sand. (it's possible that I need to adjust conditions to bring out the best in them) The DG doesn't seem to care about the other fish, but spends a lot of time poking at his reflection, so would definitely recommend a background if you get one to limit that.
Good luck!