Migrating Users,Computers,Group Policy from Root Domain to Child

Hello,

We are going to migrate users, computers ,Group Policy, OUs, from Root domain to New child domain Controller.

1. How will we migrate Users, from Root to Child: ADMT Works good but does the password will remain the same or no password will change for each user, and by changing UPN as frst it was user@root.local and migrating to user@child.root.local does user will still logon with the same user name with no changes.

2.By migrating Computers with ADMT does it will effect already Domain Joined Computers with root.local as these computer will be migrated to child.root.local domain.what will be the response of these computers.

3.How to migrate Group policy from root to child.

4.Can we migrate complete OU with user or no user will be done manually through ADMT or any best recommendation for migrating users?.

Thanks......