2 x Apple Mac pros with dual quad core Xeons, 32 GB Ram per server. Install parallels, Use OSX as the base system for security and reliability, install win2003 or 2008 server onto vm's allocate 6 gig Per virtual server. setup load balancing for the 2 vm's on parallels. Skip exchange and use osx mail services ! Use Ranger on the servers and desktop to lock them down, build a 10-20Tb Backup appliance, use NT backup and duplicate backups to another nas in a different location then to tape or ext HDD and take off site. For file shares, apps and general storage buy 4 drobo pro's or similar with 16tb storage, Iscsi and mirror for redundancy. (really simple to setup and not all that expensive! ) very fast and reliable and with regards to networking simple port trunks, spanning tree and vlans where needed.