If the tank's ready then go for it! :)
4 is reasonable for the sorority, I have a 20G so I have 7. ^.^ I recommend 4-6 in a 10G. The more the merrier, and less aggression. For babies, you won't get to know the gender. There's also a small chance of survival for them, too. They will be best on frozen foods like bloodworms, BBS, things like that. Good luck!
Over hundreds of bettas die in their small, dirty cups each day. Only you can help them live. Research and then save them, today!