Q: Using products to manage users collection/library

I have been looking into using E-Commerce for a project I am working on and am looking for some advice.

An example of the functionality I'm looking for would be a site where users can manage their own movie database. Movies would be added as products then any user can add that movie to their library. The reason for using the e-commerce module is that I would like to give the option to purchase a movie the user does not already own. The actual purchasing of a movie/movies added as products needs to be optional because we might not actually sell the movie but I would still like users to be able to add to their library. Basically purchasing of the product would depend on if we actually carry it.

I have considered setting products as a group then allowing users to "subscribe" to the product which essentially says that movie is in their library (they own it). I'm just really not sure if this is the best way to go.

Any input would be greatly appreciated!