Thanks man, first indoor grow for me, first hydro as well. I did not know they made one pot systems? To be honest the 2 pot setup i have now going in flowering, i would say you would be better off using two single pots so you can spread them out more because i have found the plants once pretty far in veg overlap eachother in the middle a little bit. As far as how big the pots are for 4' plants. I dont think you will achieve that goal without issues, however, if i can do this all over again, this is what i would do, and DEFinetily reccomend you do for maximum yield, root growth, etc. I would buy one smartvalve per tray, two 5 gallon buckets per plant, a big resevoir for the nutes, a nice tray that will submerge the pots 3" if the water was just about to overflow out, bc the smartvalve will only fill the tray about 2" i believe or so. For each plant this is what i would do, your gunna start the plants in the first 5 gallon buckets, once the roots are almost to the halfway part of the bucket you will cut off the bottom of that bucket until you start seeing roots, you will then insert this into the other 5 gallon buckets filled with the same medium (make sure the bottom of the bucket with the plant will meet up with the new medium once iserted so there is no gap, i would reccomend Coco-coir, perlite, vermiculite. These plants will flourish and grow HUGE colas if done right. This is by far the best way. Definitely get an airstone for the tray or resevoir as well