Rebuilding Flowering Room! Many questions..

Okay to start all of this off I am Completly rebuilding my grow setup .. I am changing from soil to a diy aerosystem .. I am going to stray away from my comfort zone and switch from cfls to a 400 watt hps .. I'm not very familiar with hid systems but I have done enough research to take in any advise given ... My flower room is 3 ft deep 4 ft wide and 8 foot tall .. I am doing a perpetual grow and will have 9 small plants inside the flowering room at all times .. I am hoping to keep them under 3 and a half foot tall at the highest .. I will use some advanced techniques for this ..

Now we are getting to the questions .. I need to know if the 400 watter is gonna be enough light and also what cfm do I need on my innline exhaust fan to keep the room around 78 degrees .. I haven't had to use any exhuadt in the past due to using cfls ..

All the help is very much appreciated..

C DUB

Not to keep bumping or be to pushy .. But I really need someone with experience in ventalation and hid lighting .. To answer the