Grow Cab Lighting and Exhaust

Hey im building a grow box 4'x4'x3' white paint interior and am going soil and hps lighting. I was considering 150w but i would like to go higher if the temps can take it. The exhaust i was considering was 2 exhaust fans at light level and a passive intake. I might go 12/12 from seed or do only a month or so of veg first.

Any Comments or Ideas?
CMK

if you get a cooltube it will be much easier to control the heat and you can get a higher wattage light. What cfm are your fans?

theyre 80mm 31CFM im gettin em for 1.50ea

you might want to try and get a higher cfm fan. Computer fans dont move enough air as inline fans because they dont take resistance very well. I think you MAY be able to handle 150w hps if you use a lot of fans and your outside ambient temp is low enough.