Hi kandy53 and welcome to Cruise Chat.
Congratulations on your 25th anniversary, and on your first cruise! I can't decide about which you should be more excited.
I sailed the Serenity in December 2006, and I will tell you you're in for an exceptional time. The staff is fantastic. Every Crystal person you encounter anywhere will smile and say hello. There is an incredible wealth of things to do onboard. When we sailed, there were classes each sea day in keyboarding, computers, art, and much more.
For the formal nights (this was a Caribbean cruise) we saw men in suits, tuxedos and white dinner jackets. Women were in cocktail attire. We saw more navy jackets on men during the other nights.
Make your reservations in the specialty restaurants as soon as you can, as they do fill up quickly. The meal/evening we spent at Prego was fantastic. There was a small surcharge for gratuity, something like $6 per person at the time, and well worth it.
Definitely take a sweater or jacket or wrap for the evening. Some rooms can be over air-conditioned, plus you're going to want to walk outside under the moonlight.
We did the ship's excursions in the Caribbean and were not disappointed.