Pro Sites And Membership – Kinda like Envato, same membership, different site

This site have been a huge help to me, so I’d like to say thanks first.

As for my question, I am wanting to be able to to have a network of websites that has one membership. Here is what I am trying to accomplish:

1. Anyone who registers automatically gets placed on our mailchimp newsletter

2. They will get access to a limited prosite (5 pages, unlimited posts)

3. They can upgrade at any point for a yearly fee (unlimited site with template choices and ability to add their own WP templates)

4. There will be another section where they can pay another yearly fee to access church design templates (on a single page that is protected and exclusive to paid members)

5. All on the same domain

Can I do all this on one domain? Can I have the same membership, but across different domains? Possibly domain mapping under the primary domain?

Am I crazy for asking such questions?