Sequential delivery paying course.

I need your help. I prepared a course in PDF files (audio will com later). There is 52 lessons, one for each week.
– People will have to pay to access to the courses and exclusive files.
– I would like subscibers to access to only one new lesson a week as soon as they have paid.
– I would also like my files as protected as possible against piracy, copying, … that is the reason I don’t want to send the course attached to an email.It is too easy to send to other people.
– BuddyPress forum will also be only for subscribers.
– It would be great if subscibers can download the PDF files only a limited number of time.

Do you an idea how I can do that?

I tought that maybe it is possible to do “secret password protected pages” and send the new URL by email each week. That means 52 hidden pages…..

Have a bettre idea?

Thanks a lot for your help!