we have to install a LMS 3.1 for 5000 devices in a Windows server. In hardware requirements, it says that we need 4 CPU's for this kind of installation.
My question is: can we use only 2 CPUs if we use Quad Core processors?
Yes, this meets the MINIMUM requirements for running all LMS applications on a single server managing 5000 devices. Just be aware, that sometimes the minimum requirements don't provide the best performance. Where you can improve things is with more RAM, and more CPU speed.