Best way to make marketpress more social/community oriented

I want to create a community marketplace for our area. My goal is to have every independent crafter/maker of things, locally made products in the area to be on the site. I'd like to make the initial sign up free for a while, then maybe I will charge like prosites or as a Chained payments (maybe request donations first).
I would like a site very similar to with heavy social interaction. I have been researching several threads for the last few days, I just have a lot of questions still on how to do this properly.
Here are my questions:
1. can i use prosites for membership and the chained payments for the site
2. Is there a way to showcase the substores on the main site instead of products?
3. Is there a way to use cubepoints as a way to encourage social share?
4. What is the best way to make it very social like a ning interactive site?