Well, as to sea sickness, everyone is different. I lose my lunch on small boats, in backseats of cars, etc. Don't even think about "thrill" rides. I have never had a significant problem on the ship, and I've had a few rough seas.
The ship has great stabilizers. There is a rough current between Port Canaveral and your first port--we seem to go thru it the first and last night of each cruise. Sometimes it is mildly rough, other times we've seen servers literally get slammed into walls!
The bottom line for me is that the ship's motion doesn't bother me. There is free generic bonine at the health center (actually in a container by the door) on board, and there are lots of other things you can do if the motion bothers you.