Set up a audio download site, a few questions?

Hi, I am looking to set up a audio download site with membership section and need some advice on how to go about this.

What I need is users can

Go to the site and view and listen to sample audio tracks organized by category. If they like one they can continue to purchase the full audio track by either buying credit or a one off payment.

I am not sure i want users to download the track or stream it and this is what I need advice on. May be we could have a membership system where they can store all their purchases and listen to the tracks as required.

This is only a brief overview but happy to provide any info required to get the ball rolling.