They calm down when they get older (usually but not always). Younger ones tend to be more nippy and if the one you have now is mellow and sweet, there's no telling what another ball would be like.

If the BP you have now has a very good temperment and eats well, I would definitly keep it.
It really doesn't take very long for them to get big. They also live a very long time compared to other animals. They can get live up to 40 years in captivity.