The filter is the next problem. I'm going to need some sort of off-the-tank small filter that filters at least thirty gallons, then stick a sponge on the bottom of the intake.
Nope, bettas don't eat anything other than food, brineshrimp, worms (bloodworms, glassworms, ect.), and small snails. They are completely safe except for other bettas and fish with colorful flowing fins. I woud do a planted tank with a ctenopoma species (if your pic shows a correct size, it looks pretty big to me), they don't move around a lot.