Or you can go with three switches and a router.
Id like to recommend a tip that maby you'd find useful. At the college where Im working we have two networks. One for admin and one for the students(pc labs and Library). Both have theiry own firewall. You cant access the admin side from the students network, however you can access the students network from the admin side. we have thirteen servers, but to make things easy for you. How about two servers. one server for admin and one for students. connect the servers to allow them to communicate with each other. Cos remember you'll be part of the admin and Im sure you'd like to sit at you're pc and access both the admin and student network.
Should you consider my option and need more info you're welcome to request some detail.
cheers for now
sid's