Congratulations on your upcoming cruise, and Happy Birthday! What a fantastic way to celebrate!
1. People dress nicely for dinner, but I didn't see any tuxedos, some suits, and some nice cocktail dresses, though. If you want to dress up, go for it. There are photographers on board that will do nice potraits, too.
2. Do the dolphin swim and not the encounter. You actually get to swim with the dolphins in the swim, not in the encounter. It is awesome! We did ours in Chankanaab Park in Cozumel. It is definitely one of the most awesome experiences of my live. I bought the video, so when I'm down, I pop it in and it brings back such wonderful memories. Then I can make it until my next cruise
3. Things start quieting down around 1 am, but I don't think the bars close until 2, maybe later-I've never made it that late. You can get 24 hour room service if you're hungry after the midnight buffet.
My friend went on the Dawn last spring and had a fantastic time, hope you do too!