Just moved to co-management a year ago for 10.000 clients, now moving workloads to Windows Update for Business. Below a summary of the work done.
A goo start and recommended, is (if you have the required subscription) to ask help from Microsoft FastTrack engineers to guide you through the process: https://www.microsoft.com/en-us/fasttrack
. It is an excellent service!
* Step 1: Enable Hybrid AAD Join (AAD connect) --> brings your devices to Azure ADhttps://docs.microsoft.com/en-us/azure/active-directory/devices/hybrid-azuread-join-managed-domains
* Step 2: Enable co-management in ConfigMgr --> configMgr client will do the work for youhttps://docs.microsoft.com/en-us/mem/configmgr/comanage/tutorial-co-manage-clients#enable-co-managem...
*Step 3: Tenant/Cloud Attach --> recommended for enhanced device management
* Step 4: you can now start moving workloads to Windows Update for Business.