I do not have the Carnival card but have looked at cruise cards in the past. Personally I think you would be better off with the standard 2% cash back card or the Arrival card. Unless you really love only Carnival.
No and no. Looks like it has an awful $100 sign up bonus, earns 2% on Carnival and 1% everywhere else. I concur with the above poster - you're better off with a regular 2% card, but would also add that even if you love Carnival, don't get this card.