for all g4 cube related things go to www.cubeowner.com (which happens to be down at the moment )
many people do this though i am no expert, all i can think of suggesting is 10.3 server but 'm not sure if you really need it
getting apple remote desktop would be a good idea because then you can leave it on without a moniter (and even without a graphics card) and control it with any of your macs that are networked to it