Merging two ADs - one on Office 365, the other from G-Suite to 365 - what to do?

Solution 1:

Are you using AD Office365 integration or the Azure Active Directory? I would guess GSuite is an integration.

Sounds like you are on the right track to split the migration process into two or more stages.Fortunately, Active Directory, Office365 and GSuite can be configured to be independent of each other. I would definitely only migrate one system of users at a time. For example if Office365 is the end goal maybe get all the GSuite users using Office365 Mail first. Than proceed to getting the mail domains dns records merged and straightened out. I would do the Active Directory on the computers last if it can keep running as is.