Question: Is it possible to set up several courses, and add conditionals to them?
For instance, an approval of certain course in order to be able to enroll in it?
Answer:
You can leave a course "unpublished". As long as the lessons are published, it will be available for someone to sign up.
Then, when they've completed the first course (for example, Social Media 101) you can send them a follow up email, or include the link in the last lesson (to the Social Media 201 course)
It wouldn't show up in the "All Courses" menu, but after they purchase/sign up, it will be available in their "my courses" page.