You won't know your restaurant rotation until you board the ship. If there's one MDR you're really set on attending and it's a short cruise, you might want to wait until boarding to make a Palo or Remy dinner reservation- if you're sailing on any ship other than the Wish, they usually have dinner spots (not brunch) for these available upon boarding if you have a small party and are flexible with times, even if it appears sold at during online activities booking. I've never been unable to make a 1 or 2 person dinner reservation at Remy or Palo onboard one of the Fab Four ships. Can't speak for the Wish as I haven't sailed her yet.
You can tell which night is Pirate Night by checking onboard activities booking for each day. The day that pirate makeovers are offered will have Pirate Night.