SOme thoughts. Ceiling fans are ponderous to slow down in part because of the tremendous momentum stored in the moving fan, and the free spinning bearings. Take the blades off and see if it slows faster.
Did you google "electric motor theory" maybe? Or motor basics or electric motor basics? Plenty of books at the library - yes libraries still exist.
I am no motor expert, but your idea doesn't sound right to me. AC power is already reversing hot and neutral 60 times a second. Reversing the wires won't reverse a motor. if it would, you could make your alarm clock run backwards by turning the plug over in the wall outlet. In motors with separate field and armature windings you could switch polarity on one, because it is the relative field in each that reacts to the other. In an induction motor - a brushless motor - I think to reverse it, you'd have to physically turn the field piece over.
One way to brake an AC motor is to put DC on its coil. I believe Hammond did this on some models.
Have you explored how real Leslies are built? In the typical leslie, there are two drive asemblies - one for the woofer and one for the rotating horn. Part of the Leslie sound is that the woofer is more massive and has more inertia/momentum than the horn, so the two parts ramp up and down speed at different rates. Each drive assembly is two motors - a fast motor and a slow motor. The fast one needs to be more powerful than the slow. The controls switch between them. It is more complex than that even in that the slow motor shaft bears on an idler that turns the fast motor shaft.
The traditional Leslie is fast/slow, with the transition being mechanical. COntinuously variable would not be traditional. it may be highly desirable and tradition be damned, but the original Leslies didn;t have it.