2 Focus questions. AF-ON vs. shutter release.

I believe he means that if you (accidentally) let up pressure enough and then reapply it, you trigger the autofocus to stop/start.

This becomes an issue in either mode. In AF-S, if you've recomposed, then of course re-triggering the AF would cause it to refocus where the sensor now is. In AF-C, if you're trying to track, then stopping the AF causes the tracking to stop and then needs the time to reacquire focus and/or resume tracking.

That's one advantage to the AF-On button, you can mash it with your thumb and there's no confusion as to hard you're pushing it, accidentally triggering the shutter, etc.

Yes, it should. It's just a lot easier with a separate button.