just a thought, bathroom fans are pretty cheap or easy to get used, I think they might start out at 50 cfm. I actually use one for a wood fired forge out back. Actually its a bid bottom of a boiler that I use for lots of stuff including cooking. But when I am hanging around out there, I throw some steel in the fire and I have an anvil with no horn I got for $25.
Anyway the bathroom fan has been outside for many years now and has worked fine. I agree about the dimmer switch, could work or not. I believe the dimmer switch chops voltage , so it goes to say 90 volts and drops out to 0 and then back again. So its not a complete wave form. the speed control sends the full wave form with a 90 volt peak. So small shaded pole motors will probably work, but split phase won't as well as larger amp draw... Its been a while I looked into dimmers so I could be off on that.