I don't know that it is that big of a deal. When i took mine we just used the basketballs in the high school gym. As long as you aren't using some dollar store kids basketball that doesn't ever seem to come back down when you throw it, you should be fine.
Size does matter. NCAA and NBA are same size. Anything smaller and the thrower has an advantage. The more one can grip the ball, the farther the ball will fly. This is with clarifying with the SA.