Ask HN: Starting Up A Stock Site?

I've been asked to make a stock media site that would hypothetically sell top quality stock video footage, VFX, pictures, audio, and music for fractions less (bare minimum and all original/legitimate) than current competitors. All artists would earn at least 50% from their content versus only <= 20% at best. All sales would be royalty free and there is already a good team of artists who have "signed up" and some are currently generating content as I speak. From what I understand it would be just your typical upload/download gallery to start out with and there would be a filter for professional content. Later on it might expand into new territories. Other than this limited bit I don't know much.

So my question is 1) What would I be getting into here? 2) Roughly, how expensive is it to run a stock site from beginning to end? 3) What would you want to see in a future stock site (programmers and artists alike)?

Thanks for your time.