Shows - depends on the show, how good the seats you want, number in your party, even the ship. I'd say you'll be able to find seats for 2 showing up less than 5 minutes before showtime. They may not be where you want them, but you'll find them. Doors usually open about 30 minutes before showtime.
Muster drill - don't show up late. No need to show up too early. I am usually on the early side, personally, but that's just how I roll (they start checking people in about 20-30 minutes before time listed, in my experience).
One of the MDR's is open for breakfast and lunch. Check the Navigator.
If you do your online check-in with the Disney Visa, and that's the card you have on file, your KTTW card will have a small DV in the corner. This will show the CM's that you are using your Disney Visa and you'll get the 10% off. I always double check to make sure they see it, just in case. I don't think they actually take CC's in the stores, only KTTW cards or gift cards.