Limit global marketpress categories to my network

I am creating a marketpress network, and I started thinking into the future....

100 different store owners coming up with random and off the wall categories essentially making my global categories not so user friendly.

Ideally, I would like to preset the categories any of my users can post to. If necessary and upon request add new categories.

ANOTHER THOUGHT:

Is there a way for me to create a single marketpress install, and charge users a monthly fee to post in preset categories?