Computer fans for cooling

A few questions... :o

1. Does the intake fan have to be the same size as the outtake fan?
2. If the fan is a decent make (Arctic Cooling) can it be left on 24/7, or should I get 4 fans - two intake and two outtake, and have them on alternately?
3. My closet is 2.5ft wide, 5ft high (250w HPS hanging down 2 foot above the ground though with reflector) and 2.5ft deep. What size/diameter fan should I get, and what RPM should it run at? The temp is fine at night because I have a fan blowing cool air on me while I sleep, but during the day its running between 27 and 31C :eek:
4. A 12v computer fan can be wired up to the mains, am I correct? If so, I can look up on Google on how to do this :)
5. Intake fans run level with the plants, whilst outtake fans run just above the light - yes or no?

Cheers for your time peeps :)

I can't help with all of this but here goes.
I leave my computer on 24/7 and I haven't lost a fan yet. As for wiring it to the mains, I bought a 12v adpter thing with the right ampage and wired it straight in. The adapter has settings from 3.5v to 12v so if I want the fans running slower I just move the switch.
Outtake fans should be @ the highest and intakes @ the lowest I think but I could be wrong.

your exhaust should be slightly ( within 10%) bigger to keep pressure negative, to naturally draw air in. Positive pressure should only be used when controlling temps.

and a 12v dc adapter reted for 1amp will run 4-5 12v 80mm PC fans. intakes at the bottom of room (coming from other room/outdoors), exhaust at/near ceiling (exhausting into attic, piped somewhere else...), extra fans for movement between plants and lights.