First Grow, Ventilation Question

so i made this 4'x2'x4' box for my switchable 400s mh/hps light with reflector (http://www.amazon.com/Digital-Switchable-Ballast-Reflector-GYO-2002/dp/B003810CVA/ref=sr_1_1?s=home-garden&ie=UTF8&qid=1298796477&sr=1-1) ... i dont have a cool tube or air cooled reflector... i have 1 bathroom exhaust vent fan for my carbon filter going to be placed on top...should i put a 4" (http://www.amazon.com/Suncourt-Inc-DB204-CRD-Inch--Line/dp/B004J73TAS/ref=sr_1_6?ie=UTF8&qid=1298796615&sr=8-6) or 6" inline duct fan (http://www.amazon.com/6-Inch-110VAC-250--Line-Duct/dp/B0007N5LI6/ref=sr_1_13?ie=UTF8&qid=1298796615&sr=8-13) or (http://www.amazon.com/Metal-Inline-Booster-Inches-GYO2402/dp/B003YFADW8/ref=sr_1_1?ie=UTF8&qid=1298796615&sr=8-1) on the top with a duct running into attic to suck out heat?? im going to use negative pressure and cut a hole on the bottom of right wall for fresh air to enter...im also going to have a desk fan in the top right corner to add circulation.......give me some feedback

when it comes to ventilation bigger is better, looks like your doing good though.

is it possible to stablilize temps in small box without a cooltube or cooled reflector for my 400 w mh and hps just with ventilation

haha so this was my first damn post on RIU...heres where im at on my first grow...
5 girls 63 days into 12/12....harvest in bout 2 weeks