hey man, sounds like yu need at least 400cfm fan for all that ducting, might i suggest a few things, bringing fresh air in from outside is good as long as outside isnt 95 degrees in the summer, you might have to bring cooler air into your space so think about that. and for your exhaust.... the police use this devise called a FLIR camera. it looks for heat signatures coming out of houses. its not xray so cant see through walla but they will definately see a heat signature coming from one of your roof vents.
if it were me id bring fresh air into the room from another room in the house or just from right outside the grow box. and exhause it just into the attic. you have a carbon filter so shouldnt have to worry about smells, but you dont want that hot air pumped out of a vent