Grow room setup - CO2, light reflection, isolation, air etc

Hello fellow weed growers.
I will be growing for the first time this year in a 6' x 3' closet. I have a few newbie questions.
1) what would be the perfect way to get fresh air in the room ? There are no holes in the room (although I could make one, and ventilate fresh air inside). Can I simply open the door once a day ? Would that be enough ? Or would i lose light this way ?
2) the closet is under my neighbor stairway. I will add styrofoam to isolate the ceiling, but will that be enough to cover the smell ? Obviously i will add a filter in the room.
3) can i use 1 mh 400watt & 1 hps 400watt on a regular house power socket ?

Thank you,
English is not my mother tongue so if anything is unclear, please tell me
 
I also wanted to know how many plants can I fit in my room, considering that it is 18 square foot, with a minimum of 4ft height and a maximum of 8ft (decline ceiling). I will be growing indicas
 
Top