ADFs tend to enjoy living in groups or pairs. I would suggest 2. As for aggression out of your betta -- it will really depend. Some bettas are more easy going while others can be a bit aggressive towards new tankmates. By male betta was housed with ADFs a while back, but after removing the frogs from the tank for awhile, he became a bit nippy when I put them back in. Same thing for my otos - he did great with other fish until he lived alone for awhile. But I have managed to get the frog into the tank with him, peacefully. Removing him, adding the frog, and then putting him back in definatly helped. I haven't tried it again with the otos, they were just used for a couple days to clear up some algae, and have since been returned to my 28 gallon.