So in this respect the VMs will really only be fileservers, athough the load on the servers and the network connections will be very high in the morning (when users logon) and probably very low at other times of the day. It'll probably peak again in the evening when users logoff and their profiles are saved.
I wouldn't imagine the VMs would need much memory (512mb maybe) but I would suggest creating a "bond" 2 or even 3 physical NICs to form a virtual switch and dedicate that vswitch (and thus the physical NICs) to these VMs.
Then ensure that the VMs are load balancing properly across the NICs, rather than using one all the time and the others only for fault tolerance only.
Chris