Exhaust, ventilation and smell?

I got a 4inch inline to blow out the hot air, should I get a 6 inch inline to bring in co2? Other than carbon filters what is best for smell?

the fan on the intake is kinda over kill and not really nessesary, the suction from the exhaust should draw in air through the intake just fine. and as far as smell depends on how many plants, if its only a few maybe an air purifier/freshner, but if you are doing 10+ carbon scrubber is the way to go. you can build one for around 30bucks.