We also have main seating - and yes, topsiders does the evening meals. I think they serve whatever is in the formal dining rooms.
Regarding two long days in a row - I am more inclined to do just Pisa for the day after Rome, but DH wants to do both -- and since a lot of the Florence / Pisa tour will also be riding on a bus, then we'll probably be ok with it as long as the day before Rome and the day after Florence / Pisa are shorter.
We sailed with Disney in Dec. 2005 so I don't quite feel the need to be in the dining rooms each night, although I will be any night that we're there and on time! I totally enjoyed that experience, although my kids preferred getting pizza and hot dogs from Deck 9. Dh didn't care either way.
I haven't checked to see if the port times have changed now that they have excursions out.
I had thought about a private hire for Naples and sharing a tour with another
DCL family - but with my older DS, he'll be too anxious about us missing the ship. I don't want him worrying the whole time we're out about not getting back and the ship leaving without us
When we sailed before, we left the kids on board in Costa Maya as it was rainy and we were just staying in the port area. But for this trip, the whole point is to "see the world" (or at least a little part of it), so there won't be any staying behind (and I wouldn't want to anyway with the distance from the ship to the places we want to go).