External Users vs Peer Account

Hi.  We implemented Prime a few months ago and are new to the world of LMSs.  We plan to allow customer access but am looking for the best way to do this and, long term, easiest way this would be managed.

We have roughly 1,500 customer accounts (not individual users from those accounts) that would need access.  From these accounts, there are ~18,000 individual users that use our software.

Using the External Users feature, we would have to manage 1,500 individual external user accounts and the managers assigned to those accounts.  

Using a Peer Account, we would share seats from our main Prime instance with the peer instance.  I am assuming that, in a Peer account, users (those 18,000 users referenced above) could be managed as "internal" and be managed/loaded via CSV.

Either way it sounds like there would be alot of management required.   Currently, I am a team of me, myself, and I with the LMS management (all aspects) as a small side role.  Taking on managing 1500 customers/18000 users seems very daunting for one un-dedicated person to do.

Does the community have any guidance or input on the best way to handle customer access?

Thanks,

Ray