Multisite, Pro Sites, BuddyPress, Membership…

I am building a site where people can become a member, socialize and (if they pay) get a blog. They choose a level of paying membership when they enter the BuddyPress site. (Note: there is a Free membership that does NOT include a blog.)

I start with Multisite, right?

Then network install Pro Sites… set up the membership levels…

Then establish the Primary Multisite site as the Visitor site (with its own theme).

Then create the Member/socialize/buddypress site (with its own theme).

and then…???

How do I offer visitors who want to sign up for a membership access to both the Membership (buddy press) site AND to their own blog?