What does "VM configuration required for 200 users" refer to? Please provide more explanation about what you want to configure for 200 users.
For the cross-forest migration from Exchange 2013 to 2016, you have to create mail users with required AD attributes in the target Forest B, then use the New-MoveRequest or the New-MigrationBatch cmdlets to move mailboxes, or move mailboxes in EAC. You can check this for more details about creating mail users with the necessary attributes: Prepare mailboxes for cross-forest move requests.
Here is a related blog about Exchange 2010 Cross-Forest Migration Step by Step Guide and ADMT can be used to migrate AD accounts.
Additionally, if you want to migrate mailboxes in Forest A to O365, why not configure the hybrid for Forest A directly? Hybrid deployments are supported for organizations with multiple on-premises Exchange forests and a single M365 or O365 organization. For your reference: Hybrid deployments with multiple forests.
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