Yes, we plan to bring pirate 'costumes' - actually it's mostly just black clothes with a few accessories to make it 'piratey', but it works.
Regarding the dining rotation: It's true you don't know for sure until you are issued your key card but you can put in a request, which they don't promise, but has always worked out for us. If you used a
travel agent, send him/her your request to be added to your reservation. If you booked yourself, you can call disney and ask them to add it.
Most people don't really care what rotation they get. But some like to plan to be in Lumieres for formal night, or Parrot Cay for pirate night since it has more of a Caribbean vibe. I like to remember that the 'show' in Animators Palate where the walls turn colors, has historically taken place on your second night eating in that location. So I want to make sure this falls on a day where we won't be exhausted from excursions and be tempted to skip dinner in the dining room. The dining room you eat in on the last night is also the one you have breakfast in before disembarking. For us last time it was Lumieres, and this worked out conveniently for then getting off the ship quickly, but it's a minor thing.
Like I said, I think very few people are picky about it and put in an official request, but it's fun to know the rotations and speculate/dream about it anyway.
Cindy