The problem with 'consumer' grade hardware is that you can't expect stability from it ... it is mostly designed alongwith the drivers to run 3d games as fast as possible ... like the ram even does not have ecc so an error can bring down the server easily ... I would suggest:
A dual socket system (workstation) with either 1 processor installed with ability to add another one in future or 2 processors installed
Now, you could buy a new one (lookup supermicro) but you might get a better deal if you search around for 'used' ones like the HP Z8xx or T5500 from Dell ... usually these are in excellent condition ... so nothing much to worry about especially when you'll be using new hdd!
The advantage would be ecc registered or even fully buffered ram and the LSI MegaRAID controller is usually built-in! Load up on as much memory as you can though (be sure to run memtest)!
For the software, I would suggest a Hypervisor so there is little impact of host system!
Who knows, maybe you'll save enough for RemoteFX enabled GPU and enjoy the 'full' OS remotely!