That's a lot, and I'm not gonna lie, I couldn't answer many of those. But I may be able to help on a few. Check it:
4. What level of verbal communication is generally accepted to be the necessary minimum (if there's any)?
It really depends on who you're with, and the context (personally and societally). As a small example, when I work shifts with my boss, we usually politely greet each other ("hey," "what's up," "how's it going"), but after that it's mostly silent (unless we have to ask something work related). We know each of us can see and infer what the other's taking care of, and take care of the remaining parts. But there's other guys that I work with where I know they'll be uncomfortable with silence, so we keep up a fair amount of chatter-- small talk, saying what we're doing, etc. That's really just feeling it out-- if someone seems uncomfortable whenever it's silent, you might go for some small talk.
5. How important is politeness? In interpersonal relationships, is it the same as respect?
In my opinion, politeness is paramount. Even people who arent polite themselves will (generally) recognize and appreciate it. For me, it's a matter of compassion: politeness at its core is considering how others feel and letting that impact your own actions. So that's not just "please," "thank you," or holding the door: although if those make people around you feel better, go for it.
Hope this helps! I may come back and answer some more if I have time later.