WordPress for file protection service

I’m looking for a combination of ready plugins as well as some pointers for any custom development to achieve these requirements with WordPress.

In essence, the service will be a file protection service, where customers upload their digital assets to our server. Then, these assets can only be downloaded after successful authorization through a web service call from another website.

• Customers can pay via paypal for a monthly subscription, automatically renewing until cancellation.
• There will be three subscription levels like gold, silver, bronze with different prices
• Customers can upload their files to my server for protection through a profile page only accessible by paid members. (number of uploads limited by subscription level)
• The files uploaded are stored and protected on my server; the customer can make service calls from their site to get a download link e-mailed to wherever they want.

I’m pretty fluent with PHP, so I realize all this could be coded from scratch or by using a framework such as CodeIgniter. But I’m wondering if it’s possible with WP with some paid plugins and a little bit of customization as I would like to learn it as a CMS and speed up development time.