How to set up units & integrate payment buttons


My plan is to use CoursePress Pro and MarketPress together but I have a couple of questions. Please review the link above where I these installed.

1.) I have a product/course called Torts. In Torts, I have several instructional videos. You can see them all on the live site:

If you click DETAILS on the test link, you will see Negligence and Intentional Torts set up as Units.

a.) Is this set up properly? It's weird how the units are listed twice.
b.) How would users purchase individual units and how would they purchase the entire collection?

2.) Using CoursePress, can buyers come back later and purchase additional video units/courses? How would this be set up?

Thank you in advance, I look forward to your reply.