Woah! 400w in a 2x2x?.....
Start off with something smaller, leaps and bouncds were meant for giants!
This is my setup and the average temp is around 92-93, good air circulation is important!
I have 1 175w MH the lamp is about 1.5ft from the top of the tallest plant! I used to run a 24hr schedule, but found that just 'stretched' the plant. Since space was a factor in my situation, i cant have stretching, all the space has to be utilizied. So i bumped down to an 18hr schedule using General Hyrdoponics Growth nutrients at a very-very low concentration. I grew 5 plants with this same setup in a 2x4x9 space. I am not happily on my second grow with no problems and will be harvesting those other 5 plants in less than a week!
I was told to use a HPS for flowering, but ya know what? My buddy has a 400w HPS and my 175w MH is wh00pin its butt! we planted around the same time and my plants are not only bushier but they are much more plentiful with buds than his. We use the same nutes and spacial requirements. It was setup kinda as a test, we have had fun with it, but he is kickin his ass now!
I prefer using MH to flower, even though the popular and recommended thing is to use HPS!
*steps off the soap box*
Greeny