Congrats! We are leaving this weekend for our 4th Disney Cruise. They are divine.
Absolutely get a Passporter.
Bring on your own alcohol (Disney encourages it). It will save you a small fortune.
We have found that you really do not have to book many excursions to have a great time. In fact in some ports, we do not even get off the ship. A ship with 50% of the people is a pure joy!