fan wiring

Looking on a single variac setup to control my exhaust tornado box fan wouldnt mind been abit more automated to go slow and faster when need to So what would i need to buy thermostat and some sort of relay Then the wiring what goes where? Should i wire the intake in so slows down with outtake...

anyone have experience wiring a off/low/medium/high switch to an a/c motor? i have a vortex s-line 6" inline fan that i used for a few years and had to disassemble to clean it, which btw they make nearly impossible with the rivets into plastic. anyways it's a ebm-papst m2e 068-bf 79-c01 ec...