As pointed out earlier in the thread, you're not defining requirements well.
I think you're going to want to consider setting up a cluster front-end. You generally do not want to run X on all the nodes: Let them run the monte carlo sims and don't waste memory or resources allowing users to hammer each node. Or, allow it now, and regret it later when performance plummets.
Consider GPGPU (nVidia Tesla, realizing that AMD/ATI have GPGPU options, but I am not versed in them yet) for improved performance in calculations.
Have you looked around your university? Is there anyone else running clusters with whom you could partner? My group does exactly that: We run a cluster and while I also am a numerical modeler, we provision and operate a cluster that serves users in agriculture, nuclear engineering, petroleum engineering, atmospheric sciences, HEP, chemistry and the social sciences. Your questions suggest, to me, that your time is better spent as a researcher and not as a system administrator.
And while we're here... One of my pet peeves is when a professor takes a grad student who came into a program to get their degree in, say, nuclear physics, and turns them into a system administrator and user support girl for the group. Either instead of, or in addition to, their scientific career, they have to manage the computing resources and learn how all the software works. In my experience, if they're good graduate students and conscientious, they will do a great job, but will not get the education they came for. They may get the degree, but they are likely doomed to supporting other users who got a better education. They're still good, in fact, indispensible, to a research program, but they were sacrificed with little input to their future. Better, if that's what you need, to actively recruit for someone who wants to learn the field to better become a computational expert with a discipline track in your field, nurture them, and if they are deserving, provide said terminal degree. I really don't like sacrificing an unsuspecting graduate student to the HPC gods for a faulty member's benefit.