Here's a few comments I have:

*Uploading of Files With the uc_file I wanted to keep file management to a minimum. Thus, I only added 2 operations possible @ admin/store/products/files, deleting and uploading. For a large amount of files, I figured admins would prefer uploading directly to file directory rather than using forms. After uploading, admins will see these new files show up in autocomplete file field when adding a file download feature.

*Album and Format Grouping If your file download directory has album MP3s placed in their own separate directories, you can specify the directory in the file field. This will allow customers to download all files in the specified directory. Using attribute adjustments, you can create a file download for an album directory and individual tracks that correspond with the SKU for the entire album as well as individual tracks. Mutli-format albums would work similarly to this method.

*MP3 Preview uc_file has a build in hook that would allow you to do this with some custom code. Using the hook, hook_file_action, you can add a new action to the file manager @ admin/store/products/files. In your case you could create an action "Create MP3 preview". Using the hook, it could open an MP3 file and copy the first 30 seconds of data to a file in Drupal's public directory.