MU Setup

Hey all- new to the community. I recently developed and deployed a content rich site for a client. The next phase is to incorporate secure login access, ability to purchase digital content for down-load, webinars, etc. They want to use a separately purchased URL and have it both accessible from Google search and spun from the main site.

We won't be blogging; strictly CMS with ecommerce purchase ability webinar content and digital copyrighted material access.
Does this sound like MU criteria?
I created the new domain as an add-on in cPanel. If this is in the realm of WP MU, I want to be sure I don't affect the main site in anyway.

Thanks in advance

Mike