Questions in the migration between Forest A to Forest B

Hello Team,

We have the following environment and questions, please advise.

Environment

Forest A with the following roles:

Domain Controller

Dirsync

ADFS

ADFS Proxy

Exchange 2013 onpremise server with no mailboxes hosted in it.

Has trust between Forest A and Office 365 tenant.

All the mailboxes has already been moved to office 365 tenant.

Requirement

Want to bring in Forest B

Then going to migrate all the users from Forest A to Forest B

Then going to decommission Forest A and create trust between Forest B and office 365 Tenant.

Questions

1. What are the implications and how long do we need to schedule downtime?
2. Will there be any impacts?
3. How & when can I manage (enable/disable) Dirsync, ADFS, ADFS proxy?
4. How can I transfer these roles (Dirsync, ADFS, ADFS proxy) to Forest B?

Please advise. Thank you for your time.

Balamurugan G.