How can i migrate the Azure AD users from an old Office 365 tenant to a new Office 365 tenant? Also, will it involve any downtime on the old tenant?
Also, how can i migrate the external users to the new tenant and retain the permissions?
You should look at this document from MS https://support.office.com/en-us/article/how-to-migrate-mailboxes-from-one-office-365-tenant-to-another-65af7d77-3e79-44d4-9173-04fd991358b7