There are a ton of fish that you could do. Tetras and other smaller fish come especially to mind. You could probably safely do 6 in a 10 gallon of tetras or the typical community fish but bare in mind that decorations and the shrimp and snails also will influence how much space your tank has.
Personally, I would probably do 2-3 mollies, platies, or guppies. There is one tiny consideration when choosing livebearers though - if you buy a female and a male, they will have babies and typically lots of them. The females can also accidentally come pregnant but if you buy only males, they are more aggressive and will bully each other. Personally, I'd stick with just females and then let them naturally cull the babies if they come pregnant (it sounds horrible but they will eat their own young). You can look up the differences between males and females and then choose the females in store (don't trust the employees to know which are male and female if you're buying from a larger corporation like petsmart or petco).
I also like recommending using aqadvisor, it's a stocking calculator that can tell you whether or not your tank is overstocked. It's not exact but can give you a good idea of how much fish is too much for a tank.
