So is testing positive---you do, or you don't. Degree doesn't matter. Try that at cruise check-in---"I'm just a little Covid-19 positive. Can I still board?"
When did you send it?
Embarkation day is Day 0, so the 29th is Day 2---you're good. I believe, however, since you're visiting Canada three days is not correct. Also, you must submit ArriveCAN info prior to boarding.
That waterfall is (unexpected) hot water that flows from Vaðlaheiði tunnel that was constructed through the mountain to Mývatn lake a few years ago. https://icelandmag.is/article/water-pouring-both-sides-vadlaheidi-tunnel-north-iceland
I suspect there isn't an actual door between the two cabins. There are probably hallway doors that can be closed to "connect" them---similiar to the antechamber of the aft S1's and SV's.
Ditto. That said, last May in Southampton, it was easy peasy without tags---probably even quicker. They added them at the curb (that line was much shorter than others waiting to check bags).