new to growing, need some help

hey guys, i want to start growing in my closet and i would like some help. my closet dimensions are about 3ft by 6ft. the ceiling is a little bit weird since there are stairs on the other side, so i plan to hang my lights as high as they can be, which is going to be about 5ft high. i just bought one 400w hps light system, is that going to work hanging about 5ft high in my closet?

also, what are some tips on ventilation? i plan to get a thermostat set up with a fan to blow on the lights, but i was wondering if it is okay to keep the door closed as long as the temp is correct. if the door is close is that not enough ventilation?

WEll, you have two factors. One is CIRCULATION and one is VENTILATION.
Ventilation removes heat and air that has been depleted of CO2 by your breathing plants. Well, they don't 'breathe' but they transpire, whatever.
Circulation makes the temperature and humidity the same throughout the room, and gets stale air out of the corners so it can be removed and replaced with cool, fresh, CO2-rich air.

You will want a nice blower for your exhaust fan that sucks air out of the highest spot in your room, through a air-coolable hood if you are feeling sassy (it makes SO much difference, if you haven't bought a hood yet get an air cooled one!!!!), and then out. That also allows you to run a carbon filter to reduce smells, and you will find that flowering plants reek like the day after a skunk orgy.

thanks for the quick reply, i really appreciate it. yea my hood has two round 6inch vents on each side, but i'm not still not quite sure how to set up the ventilation system. are there any pictures available so i can get a better idea?