I would be interested in finding out how you are contending with heat issues from the 400W MH. I have a closet just slightly bigger with a 250W MH and when the door is closed the temps can reach 96 at the base of the plants. With the door open during the day it is a reasonable 75. I've already cut the hole in the ceiling for an inline fan which I was going to add anyway before the flowering stage, but if I can get the temps down I would like to add another 250 to 400W light to the one I have as more lumens = more bud.

From all the reading I have done on these forums the common advice is that you shouldn't add nutes untill there is 5 sets of leaves.