Yes the License is single owner/user and permits you to have two installations Mac & or PC with one in use at any point in time.
With earlier versions there was no deactivate process but with LR CC/ LR 6 and the Creative Cloud Application I am not certain how this is monitored. I get the impression that you have to logoff from one to get the other to function properly. (i.e. The active use is controlled to one computer?)
Maybe someone in the know could clarify this issue.
Yes. If you have LR CC, the platform does not matter, one can be a PC and the other a Mac.