Contributor

Anyone see some documentation of how to go from a pure Skype for Business Online to a Hybrid configuration?

Yes, this is the article I follow: https://docs.microsoft.com/en-us/skypeforbusiness/skype-for-business-hybrid-solutions/deploy-hybrid-...

 

Basically, make sure the on-premises deployment is healthy and functional, set up hybrid, flip the DNS records from Office 365 to the premises deployment and test test test.  Then if you need to move some users down, you can as seen above.