When designing a workstation that is used to host a virtual server, you need to consider the following:
1. Memory capacity : It is very critical component of a virtual machine. The memory is required to support the host as well as the guest operating systems. More the number of guest OS's, more the memory you need.
2. CPU cores :
Again, you will need relatively larger CPU capacity for a virtual machine. The CPU cores are shared between the virtual machines, and if you need CPU intensive programs to run on the workstation, you may need multiple CPUs.
3. Hard disk capacity : Here also, the hard disk is shared between the virtual machines. If reliability is a critical factor, you need to consider disk arrays like RAID 5.
Note that other factors such as High-end cooling, HDMI output, and specialized GPU may or may not be required, and primarily based on the host OS requirements.