Using Membership with Templatic Theme

This is a bit of an out of the box help question. I have a great theme from Templatic that runs classifieds.

I want to only allow paying members to access the post a classified section.

I also want to set up a send email that will allow only paying members to communicate with each other. I don't even know where to start with this part of it.

If you visit the site http://www.divorceforcedsale.com looking at the pages that are used might give one of you really smart folks an idea as to how I can protect the site.

Membership is disabled at this point so you can see everything in it;s developing glory for the client.