Well I have a 55"x55"x79" tent and have a 4" duct fan for my intake. My exhaust fan is a 6" 468cfm with a 40" carbon scrubber. My 600 watt lighthas it's own 6" duct fan to cool it. My thoughts are to get the biggest 6" fan and size of carbon filter that will fit. Can't have too much carbon filter but too little and things get stinky. A good online retailer will have fan and filter combos that are matched together
I have a 4x4 tent. Used a single 6 inch fan and it works great with my 1k light.
The air flows in via passive intake, sucked in thru the carbon filter and pushed out thru the light and out the tent. The one fan scrubs the air, and cools the light. I dont run an intake fan because I always want negative pressure to keep any skunky air inside the tent.