Earlier quoted context omitted.
This example fails in my experience. You know not to call international in the middle of the night only after jumping through the mental gymnastics of timezone differences anyway. You'd have to do the same with a single time base.
No, you don't. You just need multiple clocks on the wall. This remains a widespread solution to determining whether or not your counterpart in Sydney is asleep.
You must always do the translation, with or without a universal time zone. The difference is that with universal time, it discards the entire set of translations around scheduling conversion that already happen, and it fixes the horrible mess of anyone living near a time zone boundary being in perpetual scheduling hell.