Re: Kotegaeshi: hand or wrist?
It's not about the wrist. One of our regular visitors is missing most of one arm below the elbow. Kotegaeshi works fine on him, provided kuzushi is achieved.
That said, the "ideal" kotegaeshi as I was taught places the pinky in the crease of the wrist. Plenty of perfectly legitimate variations exist, though, depending both on relative hand sizes and on where nage's grip happens to land.