Yes and no. They'll also work other areas (OVC, MDR at lunch), but specialty dining (like spa services, drink package upgrades, etc.) require service charge addition.
We used Europcar---a little tricky. They weren't physically at the pier location---after calling, they came and picked us up and took us to their main office a few blocks away. This took 30-40 minutes out of our port time. Return was right at the pier, so no problem.
The only negative is taxi service at the bus station is sporadic. However, Central Station (train) is only a 5 minute walk away, and they're plentiful there.
For a lower rate, you are guaranteed a veranda cabin . Typically, if you pay more, you can choose a cabin (but since you were waitlisted that option might not have been available). Your cabin assignment could come at any time---probably no latter than a month prior.
We were almost identical in Akureyri, hit Hverir, circled Myvatn visiting Dimmuborgir, Hofdi, Skutustadagigar, then Godafoss on the way back. Basically one step ahead of the tour busses the entire day. We did all this in about 5 hours.
Granted, but it's not priority (as in first served)---concierege plays the "wait for your bag number" like everyone else. The suite folks could also wait there with no issue, they never checked anything upon entry.
We use the tube from LHR, and National Express to Southampton. Lodging options are too numerous to discuss---it all depends on where you want to explore from.
I read that as if you have a supervised test, one must present a digital or physical result. Self-test falls under the portion that follows (photo or actual).