I am assuming you downloaded the Windows Automated Installation Kit…which holds the Windows System Image Manager program. If this is the case make sure in your unattend file that you set the password value for the administrator account. If its blank then sysprep will strip the password and you will be prompted to provide one during the Windows installation. This is done in pass 7 under the Microsoft-Windows-Shell-Setup_neutral component…subheader is UserAccounts.
I am not aware of FOG being able to uniquely name the computers after being imaged. If that is a possibility I would sure like to know…because that would sure simplify my issues that I am having.
You should not have any issues with the product keys for Windows since they are part of an OEM license. One thing you need to make sure of is that all drivers are defaulted to the original drivers (of your motherboard) that self-install when your machine boots. If you install any additional/updated drivers then your Windows key will be invalid after booting your sysprep’d/imaged machines. You can try the PnpSysprep component and see if you have any luck with that. It is supposed to make all drivers persist through the Windows install.