Tell your hubby not to worry a bit about formal nights. He doesn't have to wear a tux if he doesn't want to, a dark suit will do just fine. In the Caribbean that's what about 75% of the men wear anyway. Insisting on eating in the dining room will severely limit you. Sun Princess has a great pizzeria, although you can eat lunch there too. In the evening the area that is the breakfast and lunch buffet becomes The Bistro, a very nice full menu sitdown dining room. They even have live music for dancing if you like that.
The upgrade fairy is totally mysterious. In 14 Princess cruises I've had one upgrade. On the other hand, the first time I sailed carnival I was upgraded from a standard outside to a verandah cabin. If you're going to be in an inside cabin you will either need to get a nightlight in the US (currency difference) or you will have to leave your bathroom light on overnight. It's REALLY dark in the inside cabins. It makes it very easy to sleep late or nap though. Princess is a great cruiseline and I hope you both have a fabulous time.