Just keep in mind that with the big stroller, it's going to take up a fair amount of space in your cabin, which will already be tight with the crib/pack 'n play. (I assumedy you pre-ordered one, right?). Also, you'll have to by-pass more elevator rides with a big stroller b/c it'll be harder to fit the stroller, you and other folks in the elevator. Just wanted to point this out since I've been there, done that!
Also, while I totally feel best when my kids are in car seats, keep in mind you'll have to lug it around the beach while you're there. If you do take it -- and it totally has to be based on your comfort level -- you can ask your steward to store it for you. Then ask him the night b/4 you need it to get it out for you.
Let us know how it all goes!
Family Cruise Editor