First of all, I would strongly recommend to go with a Linux cluster. While you certainly can get decent performance on Windows in parallel, it is a fact that unless you configure it specifically for HPC purposes, the operating system itself consumes so many resources that it leaves less for the calculation job, not least memory. In most of my experience I see about 1.5-2x performance in serial on Linux on equivalent machines (in serial already).
I understand you are reluctant to take on the administrative Linux tasks, and you can of course start with Windows (as you say, it comes with the machines, usually) and see what you think about the performance. But don't buy 5 monitors
There are monitor switches for far less money.
Also, note that you will be working on the command line even in Windows, to run in parallel (for now, at least - we have interesting plans for ATK 12.8, to let you run on a cluster from within VNL!).