Cloud attach vs. cloud only: the debate

Background: we are starting down a multi-domain + multi-CM site merge project, and we are considering the implications of perhaps collapsing all CM sites first (migrating CM clients to a single CM site), before ultimately performing ADDS domain migrations (or Autopilot resets to convert to AAD-native when viable).

Primary question: What workloads bring the most value and/or are lowest-hanging-fruit for us to look into on the co-management workload transition journey?

Specific questions:

• In the situation where clients / endpoints from multiple ADDS domains are managed in a single ConfigMgr site (without the endpoints having hybrid joins): will Endpoint Analytics data flow from all clients (in all ADDS domains) into EA without difficulty?
• Is swinging the "Windows Update policies" workload all that's needed in order to switch endpoints to WUfB (will this work without also swinging the "Device configuration" slider)?