Can anybody help with my load balancing / server design?

Hi Im finally getting round to redesigning our server setup for our college, and could do with some advise on how to best split the services up across the servers and sites. What we have is 2 main sites with around 170 recent Macs split over them, a mixture of desktops and laptops running at least 10.5. We also have 4 1 year old quad Xserves, 1 old XRAID with 4TB, and a Promise RAID with 4TB, so plenty of kit. We are mainly a Windows based college, and rely heavily on Active Directory for everything, so more than likely, we will be using AD for the Macs. This will save duplicating data into OD, and will help with things like authentication to our web proxy and Cisco wireless. I want to keep the feel of using a pure Open Directory syetem, ideally with use of features such as the wiki and blogs, but using the existing AD accounts. So, the Xserves will not be doing anything like DNS, Mail, DHCP, or anything like that, it will all be handled by our existing Windows Infrastructure. The Mac servers will just be proving: Mac managed preferences, File sharing for departmental shares AFP Home folders for some users (mapped form AD) Software Update Server: ARD Task Server Netboot And possibly Quicktime/Podcast server. So, now I need to decide how to best split this up. At the moment I have 2 Xserves at each site, and the Promise RAID at one, and the XRAID at the other, both linked up to 1 server with duel fibre. Any ideas what you would do? Many thanks