Welcome to the forum.
Cory Cats, and Shrimp (some Betta will eat shrimp, though.)..Most say Tetras, personally I don't like Tetras, they nip fins.
Any caves that don't have sharp edges, and silk or live plants.
Aqua-Tech is really good. The Marineland one might be to powerful. If you have a Wal-Mart near you that sells 10 gallon kits, them are awesome.
I used Wardleys, but I prefer Hikari Bio Gold. I just got New Life Spectrum Betta Formula, going to see how that works.