you should be able to perform the migration in the afore mentioned way. I would suggest to alter two points:
3) Installing these packages seperatly will not be necessary, as they will be installed and configured in dependency of the Zarafa4UCS integration package.
5) As the users will probably exist in the UCS LDAP there is no need to create them again. Activating the Zarafa User Option via UDM will suffice.