Passive or Fan Intake?

I am thinking of building a 30"x30"x3 ft tall box, should I use a fan for an intake or just cut a hole and let the extractor do the work? I would assume no odor would leak out if the box is airtight and the extractor is powerful enough. I was gonna use this for the exctraction:

4 inch CARBON AIR FILTER INLINE FAN COMBO scrubber four - eBay (item 120329973727 end time Nov-23-08 12:59:00 PST)

Is this adequate, too much or not enough? I'd like to spend as little as possible with no compromises. This is my first grow. Any info (size of intake, fan specs etc.) would be greatly appreciated.

Passive

Thanks SwishaSweetz4me for your answer.