Is there any reason that you can't book the transfer and just show up at the airport the morning of the cruise if you fly in a day early?
I realize that you have to give them incorrect flight info but that is easy to figure out.
You can go by the minute the last day but it may not be worth it especially if you already ave seats assigned. Just check in when you dock using your phone, then you don't have to worry about fees.
Don't expect too much in the way of decorations. You might have a Christmas tree but not much more. Having cruised at Christmas the ship is not really decorated.
Spring break is a season. It begins with colleges the first week of March and runs through the week after Easter. Most colleges have their breaks in March, K-12 schools usually the week before or the week after Easter.