You do not have to stay at one of the hotels. There are Air bnb's and VRBO's available in the area. Keep in mind that many book up fast because of peak season. Also keep in mind that transportation will be provided to and from the hotels being used.
A dress-code that is a little less formal than Black tie, but more formal than cocktail. For women, Mid-length or full-length dresses are ideal. Men can wear a tuxedo, but for those who don't, go for a suit in a dark color such as navy blue, black, or grey.