I’d go with the mesosphere, because that’s where meteors burn up. That’s a little below the karman line and is defined by actual qualities, instead of an arbitrary number. Regardless, both exclude the ISS. :)

I like this.

It’s really the only non arbitrary answer.

Yeah, that’s probably a better metric.

Would you count a permanent base on the moon? I think it should, since you’d be more impacted by the moon’s gravity than Earth’s, despite still being in Earth’s orbit.