Base CPU/RAM requirements & per player RAM/CPU

If one were interested in buying a server to host role-play sessions or game types without a ton of addons/props, (300 props at most) what would be an average base requirement for CPU and RAM as well as per player RAM/CPU with a Linux server?

NOTE: Not interested in ads for server hosts.

Side question: Assuming RAM wasn’t a issue, how many slots could you run with a Quad-Core AMD Opteron Processor 2374 HE? (2.2GHz)

Thanks! ^^

2-4 slots a core for build, 8-10 slots a core for roleplay.

Maybe a bit more if you know how to optimize.

It’ll probably lag a lot too.

Will the GMod server use multiple cores for one server?

Yes.
http://store.steampowered.com/news/6510/

That’s multiple threads, not cores, SRCDS can only use one physical core (with two threads, one for the game and one for networking)