Seeking recommendations theme and plugins for unique ecommerce site

I am designing a new ecommerce site with a service for programmers.

After a customer registers, they may select a certain of source analysis, then upload a file to be processed. A background process is started to process the file, which generates result file. The result file is returned to the customer as a download link and/or attachment to an email.

The site will automatically charge a small fee for each analysis cycle, say 99 cents, using the customer's registered payment data.

The site will also feature a technical forum for discussion, a member's store with discounted products/services.

Eventually, we'll add ability to read and write files directly from a repository (Git, SVN, etc.), if the customer provides credentials, etc.

So, I'm looking for a recommendation for a theme and plugins that will (1) support micropayments securely and at a low cost, (2) support customer account set up and update securely, (3) interact with backend processes, passing in a file name and parameters and getting access to the output (4) provide a store and shopping cart, 5) maintain a history of customer files processed, (6) all the usual pages, posts, etc.

The beta test version will run from an existing Multisite installation, then probably as a standalone to scale up.