anything is possible, i guess. i really think your getting ahead of yourself talking yeilds right now. build your system, perfect your enviorment and take what you get and improve on that. talking 3-4 GPW before you even start the grow is just setting yourself up for dissapointment. spend some cash, get your enviormental controls under wraps. get your rez/nutrient solution dialed in and keep chugging away at perfection.
im not trying to shit in your cherios, just saying that your 5 steps ahead of yourself, and while it never hurts to be prepared theres many other factors you need to consider besides how many GPW your gonna get. you can have 20k watts but if there is flaws in your enviorment or system, genetics then all the light in the world wont get you the results you desire.