Can't register my domain

OK, so finally, I got around to trying again, and this time, the email finally came. As a "you have been invited to join the Microsoft Store for Business" email .. nothing to do with "domain sign up". 😛 

Signed out of the domain.onmicrosoft.com and into my domain.com account.

Now it asks to verify my domain with a TXT record. Fair enough, easy to do. However, to do it, I must disconnect from my current host. I guess if there is an issue, I can always reconnect it. 

BUT, I'd like to be pre-informed before I make this move.

After the steps listed here, when it says "finished", does it port my 49 users from domain.onmicrosoft.com onto the new domain.com account? Or at the very least, will the two domains will join in one organization?

https://docs.microsoft.com/en-US/microsoft-365/admin/setup/add-domain?view=o365-worldwide

Thank you!