How to hide backend store settings on multisite?

Hi.

I want to set up a site that users can sell digital downloads.

So far I have a working multisite install, with marketpress and a few other plugins.

I want to really restrict individual site admins to the settings.

Ideally they should only be able to upload products, choose categories, enter their paypal email, and a couple of other bits. Really simple stuff only.

What is the best way to do this? Can I change role permissions? if so please point me in the right direction. Any useful plugins?

Is market press right for this? or should I try something else?

Thanks