1 or 2 dwarf frogs should be fine, Just watch the betta to make sure he doesnt nip them. I have kept several bettas with adf's and have never had a problem. The biggest problem will be feeding, which I dont find hard but some people do. I just drop a nice amount of frozen bloodworms in twice a week, the betta eats a lot but the frogs get plenty and the other days of the week I only feed the betta.