I particularly like Celebrity.
I don't know what you mean by "double-barreled surname"? I'm guessing just a hyphenated name? When you first make your reservation, typically they send you an email with all the details and ask you to check them over carefully. While at that point it is the very easiest to get changes, it should still be possible. Start with wherever you booked, but if you can't get it resolved there and you didn't book directly with Celebrity, contact them directly. In any case, I doubt it will be a problem. They want you, and you've paid.
Regarding your bill, during the cruise one can go to Guest Services and ask them to print current charges out. Sometimes there is simply a printer in that general area and you can get a current bill with just your room key card. And sometimes one can track the bill on the room television screen.
If you are a frugal person, it is entirely possible to get yourself amused and nicely fed on a cruise ship without paying any of those extra fees.
I'm fine with the least expensive bottom-of-the-boat, no-window room. I've had windows and balconies and they are nice. But I've found that when I want to watch something outside like coming into a port city, somehow my view is never quite the direction I want. I end up going up to the higher levels where one can see in any direction.
I tend to do a couple excursions if they really are something I really want to do and I can't manage on my own, but often just get off and stroll about. Local museums, parks, people, stores, beaches - whatever I can reach on foot. Taking a good map, leaving a careful trail of bread crumbs, and watching the time.
Yes, the ratings and cautions are for the less able, whether they be 80 or much younger.
After the first couple of times, I quit printing all that paper also. Just the boarding pass. I don't do luggage tags, as I take either a roller bag or a backpack and just handle it myself.
The worst part of the cruise is the whole check-in procedure. They try, but in that same day they have to get prior passengers off, clean and restock the ship, and then let on several thousand new passengers. Lots of steps per person for that check-in.