Well, yes but actually no. One of the reasond behind virtualization is that you don't need the sum of resources of all machines.
At least for the CPU cores an overprovisioning is pretty common. It heavily depends on the expected load of the machines. You can run 25 idling (linux) VMs on an old laptop.
RAM however may very well be the sum of all guests combined plus a chunk for the host.
A lot of Windows performance is related to the GPU, though. So if you plan to deploy a virtual desktop infrastructure, you better have some GPUs at hand that you can pass through or at least a decent amount of cores per guest.
