I am pretty sure it is one license per machine.

Your setup may seem like overkill from the outside but I think it is best to be a little overpowered than be underpowered. Don't spend all of your cash reserve just in case you need to tweak the machines x4 once they are setup .

Don't forget to upgrade your power outlets to handle the extra load. I.E. run a new outlet (or 2) on a dedicated 20A service breaker or similar just for your gaming rigs. Last thing you want is a wall fire.