Re: ceilig fans
The classic way to do this would be to use a variable transformer to drive all eight fans. Mounting could be tricky, and it could be a code violation.
A cheaper approach would be to switch in various values of inductance in the hot line. Two units, then one unit, then zero units at full speed.
I am thinking modern fans use capacitors to control the speed though. Have never done it, but it would be fun to dope it out.