1) No.
2) I suspect you don't have priority boarding at all. What (other than luggage tags) makes you think you do? It is usually for high rewards (MANY cruises taken with NCL) members, Haven cabins, or the disabled.
3) Most people can only book onboard. Again, a perk for club "suites" and high reward members to book ahead of time.
5) Personally, I think the inside A/C areas get a bit cold. A light second layer is always recommended.
6) While I have never been overnight in the same port (on the Bermuda Joy itinerary for November), everything I can find says you may come and go as you please - as long as you are back on the ship before they leave the port of course.
10) I'd be interested in your opinion on this excursion if you do it, as that is the one my daughter is most interested in.