How can I limit how many sites a certain member can create?

Hello;

What I am trying to do is this:

I want to offer multiple membership levels that not only allow which themes or plugins that member level gets (supporter does this), but also limit the maximum amount of sites their account level allows them to create.

Here is a link to a site that sells wordpress access in this matter: http://www.wpdirect.com/cpasale/

I want to use:

Pay2Blog
Supporter
Membership
Affiliate

Together is this type of combination correct for what I am trying to achieve?

Thank you for any and all help in this matter.

best/dom
http://www.PCFmojo.com