Webpage to sell my music- could use mega help/reality check

I have osCommerce installed now, along with 3 contributions:
paypal ipn, downloads controller, and osplayer (for mp3 previews in flash)...

so far so good!

Here's the link to the cart:

https://host523.ipow.../store/catalog/

But here's the real point of this post... (and to preface this..I am a 3rd year EE major, but have no way enough knowledge to do what I want...)...
Ideally, what I want to do...which is probably a pretty big project / combination of ecommerce and CMS and just general programming knowledge....
Allow users who sign up (to the webpage/storefront/whatever). After signing up, this login is used for every part of the page, including a forum/store/CMS extras that I might have...etc.
Then, these users can upload their own beats/instrumentals, for sale on the website. It'd be real intuitive.

They upload a SAMPLE mp3 (shorter, 128kbps or less, etc.).
They upload the real download file (for after it is bought, .wav or 320kbps mp3, for example).
They submit a description, with maybe a couple other required fields that are music related/specific. I could make/define them I suppose.
They pick a price, and boom - they are done.

The beat/product would appear in the storefront. he would be added to the "manufacturers" or "producers" list (which could really just be a list of users who are registered in the system i suppose).

Then another (probably even harder part) is how the payment would work. A percentage of the sale would go to me (at my paypal address), while the remaining percentage would go to him (at HIS paypal address).

If anyone has ANY ideas on how to do this/set this up/what to use/etc. I'd love to hear it. Or if anyone wants to take on a big project with me...hey that's great too! haha.
and I know, "why don't I just hire a real programmer" ? Well, $$$ as usual. I can't spend it now, but if this site were to start doing well for itself, and I DO imagine there is a pretty decent market for this...I could always include any helpers in payments that I'm getting! haha. if anyone wants to do some volunteer work, at least for the time being...be sure to let me know. ha.

anyway, thanks for any comments anyone has.
solo