Trying to figure out the why of anything RCI does just leads to frustration. It has been repeated many times on the RCI boards about this issue - book for two to get around the increased solo pricing issue and then if you want the extra C&A points for solo, change the booking to a solo later.
Like Harry usually does, be mindful of the potentially bandwidth challenged readers - limit the number of pics per post (CC used to limit that to six) and if posting after the cruise when easier to do, lower the resolution of those pics.
Yes, it's one of the steps when booking unless for some reason it's "sold out" and are forced to late seating. Be advised, RCI's version may not be the same as other lines.
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.