ok well, I'd say a 2x2 space with a 150w would do nicly with 2 plants. If you plan on using some good seed stock, and DWC, you wont have very long to wait.
I'd also suggest implimenting some training(bending, tie-down, lst, ect.), and selective prunning(topping, fim, and not to mention the occasional(sp?) removal of or tucking of larger fan leaves).
If ya keep at it, you will no doubt develope your own style in time. Just the things that make your garden fuction the way it does. Who knows....you may find out that one plant will fill the sweet spot!