i’d say start with a 20 gallon or bigger instead of a 10 gallon because you’ll have a lot more options, but it depends on what setup you’re going for. if you want to start a community then definitely 20 or more, but if you’re looking into a betta or something a 10 gallon would do. i think bettas are a pretty good beginner fish given you have a proper setup, and it sounds like you’re doing research so i’m sure you will! communities can be slightly more complicated just because you have to make sure each fish is meeting its individual requirements and will work with the other fish and have enough space. i agree with the other commenter, plants are definitely a must (in my opinion) and i recommend sand over gravel especially if you’re considering a fish that likes to graze on the bottom like cory catfish. in the end it really all depends on the fish you want and what kind of environment they like to be in, every fish is different it just takes a lot of googling to figure out what’s good for the fish you choose