Well, I'm not the best with stocking ideas, but here goes.
In my 40 gal, I have a school of tiger barbs, a school of cherry barbs, a few upside-down catfish, a pearl gourami and some mystery snails. So you could probably do something like that.
You could do guppies and corydora catfish if that's your jam, you could have different color variants of guppies and any type of cory you'd want in a tank your size. That's how I'm running a 10 gal at the moment. 3 male guppies and 9 pygmy cories.
A good website is
AqAdvisor - Intelligent Freshwater Tropical Fish Aquarium Stocking Calculator and Aquarium Tank/Filter Advisor. You put in the tank size, what fish and how many, and the filter if you want, and it'll tell you if they're compatible, if they'll be okay in that tank size, what perameters you should have, etc. It's super helpful!
I also buy a lot of stuff (fish, plants, and all of my mystery snails) from
Aquatic Arts - Unique Fish, Inverts & Aquatic Plants by Mail!. They're a little bit pricey, but the quality is worth it. They have a live arrival guarantee, and they always send extras. Having a local fish store (not a big chain) that's reliable is also really helpful. If they're good, they'll answer your questions without making you buy from them.