True but if you can't do it, you are pretty screwed.

This is a pretty good detail. Makes the story a lot more interesting, and deep.

Not if you hold the power button. Yeah if you single press a power button, the os can divert that, but long press, the SMC will cut power. Similarly how, pressing and holding the power and the volume down button on a phone, cuts power, even if the OS is hard frozen. Sometimes you just need an emergency exit.

I don't, but apple does. This is why the touch ID is in the keyboard. To be fair it does come as a unit if you buy the mac new.

I assume there will be a power button on the keyboard or mouse. This is just sort of a backup.