If you use the migration wizard you can choose a single person or two to migrate/move over to Exchange. You do not need to migrate the whole server.
You still need the Exchange Notes Connector to allow communication between the two domains. This Connector will provide you with the ability to share address books (Exchange Global & Domino Public), also provide you the ability to exchange messages between Domino Users and Exchange / Outlook users, and Calendar invites.
I've performed many Domino to Exchange and Exchange to Domino migrations. The first step in any migration is to do a pilot. In your case you will be going from Domino to Exchange, you need the connector and you will need the wizard. These tools are free and come with MS Exchange, and they are the only way to ensure that the data is migrated/moved to the other environment - without doing manual entries.
If you have any questions on how to configure the Connector and how to use the wizard, I will be willing to assist off line. As mentioned I've done these many times before and probably have a complete project plan with steps and time lines in my document archives to help you in this adventure. Here is my email:
Rick_Platt@hotmail.com