How do I set a default theme for my multisite users?

Hi,

I want to setup a default theme for my mulitsite subscribers with specific admin permissions. What is the best way to do this? Is there a plugin?

I need the following:
1. Default theme so the subscriber don't have to set it up themselves.
2. Andmin permissions such as products and posts (only).
3. Block all access to the other admin files.

Thanks!
3.