subdomains, domain names, & domain mapping with multi-domain

I have as the main domain.

Also there is,,, etc.

I am able to make, and basically without issues.

Is it possible to create without a subdomain? Would I need to create and point to that subdomain?

Can we create and and in addition still add,

Worded another way – once we enable multi-domain do the sub-sites on the WPMU network need to have a subdomain unless it’s I.E. Additional domains must be a subdomain on the network or a pointing to a subdomain on the network?

Happy Monday!

– David Monk Sr