Membership Subscription help

Hi There,
I'm trying to find out how to best use the membership plugin to suit my clients needs.
This is the scenario we need to achieve. There is no cost involved with our subscription, it's an online course which accompanies a Yoga School, which handles payment.

We have 10 membership levels. ( Level A thru J)

Each Level has it's own content available to it specifically. Content A is only shared with Level A, Content B only with Level B etc..

And our Course subscription, starts with Level A and ends with Level J. Each Level expires in 30days, and we'd like the user to retain access to this level after 30days, yet also pass to the next level.

Should we be selecting 'serial' for the subscription mode? or 'indefinite'? I can't seem to find out which will do this for us. Or is this not possible at all?

Thanks for your help!