You can enroll in one trimester at a time, and it's ok to take breaks in between enrollments if you choose. 

You can choose one payment, or four monthly payments. If you choose the payment plan, you are responsible for the payments regardless of whether you miss sessions, or any other reason.

You will still have access to the material during the "fallow" month, even though you will not have to attend live sessions during that time. You can use that time to review cases, or just let it be a break - whatever is best for your brain in the moment!