active directory - How do I properly setup a new hybrid exchange server in a new domain and new Office 365 tenant?

Current setup and background

We are changing our company name. With that means changing our internal domain name, email addresses and Office 365 tenant. 100% of our mailboxes are in the cloud (Exchange online). We used to be on prem but migrated all mailboxes to the cloud. We manage users through on prem AD and ADsync them to O365. We kept the hybrid exchange server on premise because Microsoft recommends it.

The steps we are taking to accomplish this are

1. Build a new internal domain


2. Create 2 way trust


3. Migrate AD objects using ADMT


4. Build new on-prem Exchange server and populate with old domain user data



5. Purchase new Office 365 Tenant


6. Migrate O365 data using 3rd party tools

My question is related to step 4

Given the fact that we have no local mailboxes and everything

• What needs to be setup on the new on-premise Exchange server to function
  
  properly in the new domain?


• Do I need to extend the AD schema to include Exchange attributes


• How do I populate the Exchange attributes for the users after I migrate them
  to the new domain (ADMT does not migrate Exchange attributes)


• Can I bypass this all and just not have on-prem hybrid exchange?

Answer

Seeing that you're moving to a new O365 tenant I don't see that you need on premises Exchange at all. You won't need any Exchange attributes on premises. You'll manage all of your mailboxes, distribution groups, etc. in Office 365.