Themes on multisite network

Hey,

I have installed the pro-sites plugin and basically I have bought the premium theme for the main site. Example domain.com.

I want to use that premium theme on root domain but don't let other users to be able to use that theme.

Furthermore, let say I give two options to signup (free & paid) and I want to let free users to have access to certain themes and much more access to paid users how can this be accomplished?

And can a user (not the super admin) buy a theme from the marketplace and install it on his own site (site.domain.com) by himself?

Your input is highly appreciated.