“pre-packaged” Drupal sites

Hello,
I’ve got a passive income idea in which I’d have users from a particular niche come to my website, sign up for an account and pay for a service which lets them choose from certain pre-designed templates, and get their own “pre-packaged” Drupal site. How do I do that? I know that’s a rather BIG question, but I’m not even sure what terms to start searching for!

I do know how to create the basic functionality of the templated/prepackaged sites I want my users to choose from (i.e. a blog, picture gallery, email list, and several designs/themes), and I understand there is a ecommerce module that allows for subscription based payments – but I don’t know “offer” those pre-packaged sites to users? That is, how does the user go from signing up for the service and choosing a prepackaged site to actually getting access to one of the prepackaged sites? How can those sites be set up automatically after the user has paid a fee and chosen a template?

I also have questions about the domains associated with these sites as I’d like to offer my users two choices: a subdomain from my site – or the ability to use a custom domain.

So, I guess I have three questions:

1. How do I set up “pre-packaged” Drupal sites for my users to access?
2. Where can in find out information about domains, subdomains and hosting for these pre-packaged sites?
3. And most importantly - in my Drupal/Google searches, what sorts of terms should I search for to get questions 1 and 2 answered?? Where do I begin?
   

I know what I want to do, just don’t really know where to start looking! Any help would be appreciated! And FYI, my PHP and MySQL skills are currently pretty light, but I suspect I’ll probably need to get my hands rather dirty to pull this off!!

Thanks!!!