I have a client that did the same itinerary on the Dream. They said it was the best cruise they had ever been on. And for me, the Sun is one of my favorite ships, so put it together and everything should be wonderful.
As for tours, yes, NCL tours are pricey as are most cruise tours. We have always booked prior to sailing with indepenant companies unless time is a concern. If you are looking at tours that will run close to sailing time you are better to spend the extra and book through the cruie lines.