Servers have a few features that desktop PCs usually don't have. A dedicated IPMI interface such as HP ILO or Dell iDRAC. Servers also have dedicated RAID controllers. In datacenters today, most servers are virutalized. So, you want hardware with a lot of RAM. Then run a hypervisor and several VMs. Get an add-on NIC card and work on dedicating individual ports on the NIC to individual VMs.