Creating an Mp3 Download multisite... Help!

Hey guys,

I have been trying for months now to figure this thing out on my own. Im now ready to swallow the pride and ask for help. The easiest way of explaining my project is to show you a website thats incredible close to what im trying to do:

makehitmusic.com

The differences on my site would be Super-Admin could:

Upload Flash Headers (different for each producer)

Restrict Access to Individual Plugins Based on levels of Membership

Another difficulty I'm having is finding the proper cart that will (like the site supplied):

Accept Producers Input for Price and Link To Downloadable Product

Posting should Auto Embed this mp3, description, and Buy Button

A link to some of the required features I should have is here:

makehitmusic.com/sell_beats

Some of the features on the previous supplied page are obviously easily attainable by use of plugins, this is just a reference to detail out the primary idea. I need to get to the juncture of the site supplied, then be flexible to add new features via plugins for my site owners.

Last, I'd like to have Templates set up to be automatically used for each Membership level (different plugins and pages created off a template).

Thank you for any help ahead of time!!!

David