I'm going to have a go at this from a different approach. What is needed is to enable a product to be entered as an event. That is all, tres simple.

As a product it has all the features of a product and can be added to the cart etc. As an event all that happens is that it gets to appear on the calendar.

The signup module only sends out emails and that's about it.

I'm also going to create a uc_groups which will be similar to uc_roles, signing the user up to a group instead of a role, so that they can have access to private material.