Music Script Modifications

My project is a music script that I have, which allows admin to upload music/audio tracks for sell online. The problems i have are: 1. The upload system sucks as I have two files that need to be uploaded, One - The Preview song and 2- The Full Song only available after successful payment. Well for some reason, after a long wait for upload, some songs will not even play from the frontend. 2. the other problem is the Paypal integration. Right now, upon successful payment, a download link is suppose to be sent to the customers email address he used at purchase, but this seems to only happen when it wants to? Will take any suggestions on what could make it better. Small budget but I have many other projects if I find someone willing to help out