Need some ventilation systems advise

[Hawkeye]

I picked up an old Jennair fan from a customer. Used it to build my 4' x 4' welding hood. Not too loud and moves a lot of air. No hurricanes, though.

If you want to control a DC motor, I'd suggest Pulse Width Modulation, rather than mere voltage reduction. Make sure the PWM unit runs at a frequency above audio. Keeps you from hearing the pulses.