Typically, most micro servers don't need more than 2-4 CPUs.
The processor type is not the limiting factor, in so much as the rack size the board is going into.
Typically, large scale servers incorporate several racks of 2-4 CPUs per rack to get to the large numbers you see advertised like 512 CPUs or 256 CPUs.
Those units are massive, and take up a lot of space.
Hope that helps.