A few bowls will do and daily water changes while they are in quarantine are recommended. If they do get sick once they are in a sorority (sometimes one is all it takes) you have those bowls to fall back on.
Yes we do have a sorority. The thread you keep following is actually an account of our first attempts at making one. Needless to say it didn't go very well. *knock on wood* We seem to be doing a little better so far, but we're still having some bumps and bruises along the way.
Piece of advice number one: Quarantine is your friend when you get new fish. When we first got our new batch of females we had them quarantined about two weeks to watch for diseases (esp. columnaris b/c it tends to hit newly arrived bettas very hard and is extremely contagious) and it gives you time to get a feeling for their different personalities. You want to keep them in their own separate containers, not just separate from other species of fish.
Stay tuned for more advice...
PS-Starving_Poet is a good person to friend/ask too