What are the minimum required fields for an unattended Windows Server 2008 R2 installation via Windows Deployment Service for the ImageUnattend.xml portion?
The absolute minimum settings are documented here Settings to Use for an Unattended Installation Note that these would be in WDSUnattend.xml. Technically speaking you don't need any settings in the imageunattend.xml file. It just means that you get to go through setup after system install. To automate the OOBE portion you need at least the following sections listed here ( Settings to Use for Automating Windows Welcome ) and tagged with server 2008.
I've never tried just the minimum as I've always tried to do as much as possible at deployment.