Migration Manager for Active Directory

Migrating multiple domains into a new domain

Hi there, 

I am migrating multiple domains (SourceA and SourceB) into a new 2016 AD Domain (TargetA).

I want to migrate all the users, groups and workstations into the new TargetA Domain leaving Exchange mailboxes on the SourceA Domain.

I want to use only one migration account, that is, a service account on TargetA Domain, say TargetA\svc-mm

I have added the account TargetA\svc-mm to the Built-in Administrators on SourceA Domain, SourceB Domain and TargetA Domain.

Does the migration account TargetA\svc-mm needs more rights than those? 

I know in the installation instructions have it more complicated than that, with migration account on the source domains as well, but I am not sure they are needed, are they?

Thank you,