help with getting proper ventilation

I am building a box, it will be around 45' across x 36' deep x 78' tall and I will be using a hybrid suntube-reflector inline cooled 400w hps setup (the closest one I could find). http://www.ebay.com/itm/6-Horizon-Binary-Air-Cooled-Tube-Reflector-1000W-HPS-Hydroponic-Air-Cool-H055-/281078400245?pt=LH_DefaultDomain_0&hash=item41719404f5 . If I use this exhaust fan and filter http://www.ebay.com/itm/8-x-26-Carbon-Air-Filter-Pro-Combo-8-Inch-Duct-Fan-Inline-Exhaust-F024-/271206142826?pt=LH_DefaultDomain_0&hash=item3f2525536a . how big should I make my passive intake to get proper air flow? thanks.

That is a massive filter for that space, You can get by with a 4" from the same place(Gotham), go with the pro model (4x18x2) , as it is thicker walled (2" of carbon, not 1.5 like most) and refillable. You will have a hard time with negative pressures going with a fan and filter that big. As a rule of thumb, intakes (passive - natural draw) need to be at least 2x if not 3x the exhaust size. My grow room is 9x4x7.5 and that little 4" fan and filter is more than enough. I have 2 actually, 1 just scrubs the air in the room and the other is an exhaust fan for flowering. I use a small axial fan for exhausting when in veg, growth to save my carbon filters for when there really is a smell. A small 200+cfm axial fan ($20) for the light fixture by itself will be all the fan you need for that light to keep it cool to the touch and you will have less temp swings to boot.

Plus once you go with a smaller fan, you won't need nowhere near the intake holes to riddle the cabinet and cause potential light leaks as well and save as much internal space on the cabinet as possible.

Peace and Great Grows

Asmallvoice