Given what individuals Bettas are, that might also depend on how territorial your male Betta is. I can see several female Bettas and some cories getting along really nicely in a smallish tank. We have lovely coloured females on sale up here. Believe me I've been tempted! My Jack Sparrow views anyone and anything in his 5 gallon including the snails as potential rivals or food or trespassers, including my finger if I have to replant a plant. Eeeeesh. But most Bettas seem to just grandly swim around, knowing they own the place and cories wouldn't be any threat to them in the male model category. So good luck! That being said, I love my Cories, they are super cute!