Develop Requirements - audio loop ecommerce website

I would like someone to help me develop very clear project requirements for a new e-commerce website. The deliverable is the Requirements Document and scripts for the new website project. Here is what I know so far: The site will be hosting & selling thousands of audio loop files (WAVE, ACID, REX, maybe others). These audio loops are used by musicians to creates songs or sound tracks. The site will be somewhat like iTunes, but for audio loops. It doesn't need to run on the desktop like iTunes or sync up with any devices, but the categorizing is in the same theme. We'll reference iTunes for good ideas. We want users to be able to search for styles and types of audio loops and then sort/filter on various categories of files. They might sort/filter on time signature, tempo, key, instrument, number of bars and other descriptive catagories. They will need to be able to audition some of these audio files. Users will likely want to purchase groupings of audio files not only a single audio loop file. Once purchased the users will download the files they've purchased. We'll need an e-commerce order processing engine. We'll likely want to remember what files they've purchased so that they can re-download them at a later date. Many audio loop users have thousands of loops typically on CDs. We're approaching this differently with a website instead of CDs. We'll want the site to make recommendations based on their selections, past purchases and others selections of similar files that others have purchased. I'm sure there are some good examples from Amazon that we can reference. This is a very general overview. I need detailed assistance developing specific requirements so that I can set the proper expectations for actually developing the website. I plan to put the overall project up for bid here too once I have excellent requirements in place. The deliverable for this posting is the "Requirements Document" and scripts for the new website project. Thanks for reviewing this!