Well, 1 thing is certain, you aren't using up 20,000 notes in 40 measures. That'd be 500 notes per measure!
One question of curiosity. Does the number of tones per patch or part have anything to do with notes? For instance, if you run a part that uses all four layered tones, is that taking 4 notes per key you press on the sequencer? I know it works that way with polyphony, does it work that way with the sequencer?