[tor-relays] Limiting Tor Resources

When setting up a relay, we are told that Tor doesn't scale well beyond dual core systems. So with me having a 6 core CPU, is there a way to sandbox my relay and restrict system resources to say, at most 2 cores(4 threads) and 2 gigs of RAM? Now I know simply setting up a virtual machine could solve this, however I've had no luck getting the ORPort and DirPort to reach the outside world. Probably missed something in the Tor relay or KVM(hate virtualbox btw) documentation.

-AceOfSpadez79-