If you get upgraded that close in you'll need to get a new tag from the porters at the terminal.
The denial email usually comes the day before sailing. You should see the status if you follow the original email offer link.
Welcome to CC.
Yes, you just need the three booking numbers.
If you care about C&A points, move the person with the most points to the interior cabin and confirm it's booked as solo.
Payment status has no bearing on ability to book things. Ask others on your sailing in the Roll Call thread if they are having issues with your particular sailing.