You should be fine staring with the MySQL eCommerce DB that we offer. If you have not seen it already you should take a look at the Digital Goods Download Center guide that we have here:
It references the eCommerce db within this guide and is intended to help you come up with a download center like you have described. Please give this a look and the other docs that it references to get a better understanding of the exact steps you will need to take to implement this. Let us know if you have any difficulty with this or if you have any questions.