None really. It just a matter of seeing the musical/show before or after dinner (provided you want to see the shows ...... and you should)
Some may argue that the wait staff is "fresher" on the first seating, but they have been working all day, so it not as if they have been resting up for dinner service.
Even if you do not stay at WDW, I cannot stress enough ARRIVE AT LEAST A DAY EARLY. Do not try to fly in, in the AM and go to the ship. The last thing you want to do (especialy since this is such a special trip) is miss the boat - so to speak.
I also recommend against the WDW bus service. It is nice, it gets you to the cruise terminal, and if they know a busload of WDW people are delayed, they may just delay the ship (maybe) However, the WDW bus service gets you there when they feel like it, in the afternoon. By the time you get there, there is a good chance the ship has been open for boarding for 2-3 hours allready. What is so bad about that you ask? Well, first that means 100's of people have hit the excursion desk and booked any remaining shore excursions (of course you can book your in advance on line). It also means that the ship, and all its attractions have been "open" for three hours while you have spent your time waiting for the bus. Do yourself a favor, spring the extra $50 or so over the bus for car service, and get to the cruise port early, and board as soon as you can.
Just like when you fly, take a carry on with bathing suits and other sundry items. Then board the ship nice and early, book your excusions, go to your room and change, grab a drink. And then you and your fiance relax poolside while thinking of the people who are still at their resort at WDW waiting for the bus
-dave