take into account that if you buy license for your PC, the license will not be avaiable on the virtual machine. I mean, a virtual machine its a different PC
A VM is like you install a PC inside your PC, so for that you need a SO + product key. I recommend you to watch some videos on youtube, there you will find how to install it and so on.
About the ram, it depends on how much ram you put as you can decide how much your VM will have, the same goes to the number of processors. The more you put, the better it will work.
Here am i installing win7 on vmware.... No BG bots so lets bot on the VM