an inline fan looks like this
CAN-FAN 8 INCH HO 737 CFM INLINE FAN FREE SHIPPING - eBay (item 110315520711 end time Mar-21-09 06:47:10 PDT)

you dont need that big of one, its just to give you an example. there are other brands and cheaper ones out there too. i would go 6 inch. you just hook up ducts to the fan and to your hoods and to your carbon scrubber for odor if you need one. it will suck out all the heat from the lights. also if your growing in a closet you can do with out the mylar and just keep your walls flat white paint. which it prolly is already painted that color. just mylar the closet door, which will save money. also i think you asked about climate control? when i use to grow in a closet my fan just sucked all the air up in to the attic and drew air in from my air conditioned room. i had no heat problems with that set up. i didnt need an extra fan to bring in fresh air with my passive intake duct. and yes if you want to utilize all that space i would get 2 400watt setups with aircooled hoods. the air cooled hoods are mandatory cause it will get way to hot in there