In My experience we always had 3 workspaces for Dev, QA/Testing and Production for each functional area or planning area. So if you have Finance and WFP use 6 workspaces. Recommended Size of workspaces will be in the order Prod>QA>Dev.
Except all these keep separate ones for datahub( Dev, Prod and QA) because that will simplify your entitlements.
Although these are not defined best practices but this setup works and is easy to maintain.