..."W" & "N" are all about seeing the ball, and like you said, once the pitcher starts to go into his motion, that's all that should be focused on.

"I" is about timing, so if the hitter's late (and they are rarely early) they can adjust by starting their swing earlier, but that should be thought about out of the batters box in between pitches.

When I'm coaching at 3rd, I really just try to emphasize watching the ball hit the bat. If they're swinging at crazy garbage pitches, I might try to remind them we're only looking for good pitches. Maybe encourage them to start their swing early if they're really late. That's about all a coach should do in a game, though, IMO.

Everything else, mechanics, stride, etc. should only be done in practice to try to develop good habits. This also needs to be carefully explained to the players, because often they will struggle to understand this and paralyze themselves at the plate during games by thinking too much.

And yeah, those grandpas in the stands drive me absolutely crazy for exactly the reason you mentioned.