Creating a Marketplace with Multisite

Hey Everyone

So, I am interested in the possibility of creating a marketplace on Wordpress Multisite. But not a traditional one, so let me explain a bit.

I have Wordpress multisite set up and will have users sign up for User accounts (not admin accounts) in which they can post items for sale using a front end form plugin I found. However, I wish them to be able to accept payments via PayPal and would hope to also take a percentage from it.

Now, I do know you have MarketPress but when I tried using this with my particular theme, adding "products" did not become "posts" on my site and to top it off it isn't compatible with WP User Frontend plugin im using for members to post with. I dont want members in the admin area.

Does anyone know if this type of thing is possible or if Marketpress could be made compatible to use with the front end posting form from WP User FrontEnd? Thanks in advance. Oh and FYI I am using Snapshot Premium theme.