The Chorus and Vibrato is caused by the Vibrato Scanner in the organ. The Chorus setting on the organ is actually a shallow fast vibrato. C-1, will give you the shallowest form of Vibrato. C-2, will give you a bit more depth. And C-3 will give a good amount of depth. The V-1/V-2/V-3 settings are slow, and full of depth. They don't particularly sound nice through the Leslie on fast. But sounds pretty creepy through the Leslie on Slow!
The Main, Echo & Ensemble on the Leslie switch was originally designed for Organs with self contained speakers. Like the A-100, and other brands of Organs as well. The Main, would play sound through only the Leslie, Echo would make the organ play sound through only the Speaker Unit in the Organ, and Ensemble would play both the internal Speaker & Leslie at the same time.
Percussion temporarily plays the 5th or 6th drawbar I believe, to give a punch to the sound, like a piano. You mimmick percussion by using a setting like 666080000, but the 5th harmonic doesn't decay like percussion does. It does add bite to the sound if you got a C2/B2 or other Model without Percussion, though!