Jungle has no idea. 4Kw is PLENTY for that space. That's 1Kw for every 4'x4' area. And the size of your plants has to do with your grow style. If you're going SOG, you'll have shorter plants and more of them. If you're not wanting SOG, you can fit fewer larger plants in there. Of course, ultimately the height of the plants is limited to the height of your grow room, but you get what I'm saying (I hope).