Could really use some advise here, PLZ....

Ill try and make this short. 2x4x7 tent,400 watt air cooled light so far. Do i run a exhaust fan(6" fan/filter combo) for light/carbon filter and is there a timer on this? Then to make sure the tent recirculates air every 5min. or so, do I use passive intake and ANOTHER say 4" (cfm's ???) exhaust when the light fan is off. Trying to find the right combination here without having to re-buy something. I look to this site as a first timmer and appreciate the advise from seasoned growers. Thanks guys and gals.

I'm not sure if that has a built-in timer, you would probably have to get another, but your plan sounds pretty good, it should work fine!