My wife and I traveled on our 4th cruise together and left the kids at home. It was a relaxing 10 days and we enjoyed our trip. We flew into Fort Lauderdale and took a taxi to Miami - mistake...very expensive. Find a shuttle. We always arrive a day early and Miami was fun the day before. Enjoyed south beach.
Embarkation was easy. Arrived at noonish and were on board by one or so. Excellent curbside service with bags.
The sun is a small ship which is nice in many respects. No large crowds and it really offered everything we needed. We spent all our time on either the 6th floor or top/pool decks.
If you don't like long corridors and easy access...6th floor is a decent spot.