For the 1st Question :
As per the docs it says you can for 4 mgmt domains or 4 workload domain but we can't federate WLD with mgmt. domains. The main reason for this is to keep management components separate from WLD components.
2nd Question : i think it design choice I would assume but within those 2 regions you could have 2 AZ's. So, would be 4 management domains.