i'd say PW along with the message store configuration wizard would be the most critical components during this. always make sure to run PW with a proper account.
# Log on to the Cisco Unity server by using an account that:
* Is a member of the Domain Admins group in the domain in which the Cisco Unity server is being installed, or that has permissions equivalent to the default permissions for the Domain Admins group.
* Is either an Exchange Full Administrator or a member of the Domain Admins group in the domain that contains all of the domains from which you want to import Cisco Unity subscribers.
Caution! If you try to run Permissions Wizard using an account that has less than the default permissions for a Domain Admin, Permissions Wizard may not be able to set all of the permissions required by the installation account and the services accounts. If Permissions Wizard cannot set all of the required permissions, either the Cisco Unity installation will fail, or Cisco Unity will not run properly after it has been installed.
if users are going to be imported from different OUs you need to do that in the PW, actually you can look at it here:
http://www.ciscounitytools.com/HelpFiles/PW421/PWHelp_ENU.htm#Exchange
step #22
the MSCW would be just to make sure the permissions updates are reflected for the exchange and in case the users are going to be in a different mailstore
HTH
javalenc
if this helps, please rate
HTH
java
if this helps, please rate