in my opinion there is no need for the dimmer for the fan....from my experience there isnt a such thing as too much air flow, but there is a such thing as not enough....

In my opinion the dimmer is unnessicary especially with your setup, you can just use passive intake with some kind of filter and like kony said make sure its 3x the size of your exhaust and you shouldnt have any suction problems.

you want your fan to be pulling as much as possible the way you have your ducting setup with your carbon filter

alright talk to you some more about this in chat