Is your main computer at least a dual core? Also what is your main computers video card? Honestly if its a dual card and you have a fairly decent video card you could run all three on that one machine if you liked. As stated keyclone and octopus will handle all your kvm/key replication needs if you decide to use all three computers and honestly I would probably start by trying to use all three computers. It will definately decrease any lag you have in cities / pvp. Depending on the answers to the above questions you most likely have a 5 boxable setup as well if you wanted to move up later on. With three boxes you could do a 2/2/1 setup on clients between your three computers.