They can vary in size. I have a killerbee who isn't really much bigger than any of my big males.
Though I have a calico girl who trumps them in size!
Ball pythons don't really get so big that they become unmanageable, unless they have a bad attitude. Make sure you ask how the snake's temperament is. Often times, breeders don't handle their babies much, so it may be difficult to get an honest answer.
I think the Hypo Vanilla Super Pastel would be an amazingly hot pickup! Very hard to find such specifics though. Good luck!