How to restrict website theme and plugins per user

Hi guys,

Basically, I want users to be able to "shop" for pre-built websites on my website. These websites will have set themes, plugins and widgets that the user cannot control. They are only able to edit the content within the website.

Once the user has found the website they want, they opt to purchase it and then are taken to a user registration screen and select their domain name (which they can map if they need to with the installed Domain Mapping plugin). They are given a log-in and their website is live. They are then able to go in and change the content within the website to suit what they need.

My WordPress is set up as a multisite install, but I'm just unsure what plugins to install for the requirements of my website.

Any help is much appreciated!