JSW...we're in NC as well. I would certainly winterize your freshwater systems but you shouldn't have to worry about your engine systems if you are going to be on the boat and able to run the engine if we get a cold snap. The salt water should not freeze. Ditto the head system but I would certainly keep the through hulls closed then you are off the boat. I assume you'll be plugged in at the dock so you can keep your batteries topped up. Run the engine when you're aboard. Keep the cockpit scuppers clear as debris and ice can form there and sink you!
This all assumes you will be in close proximity to the boat and making regular visits. Even though the bay waters don't freeze here, fresh water will in a good cold snap so if you can't be there to pay attention I'd do everything Casey says above except for the engine.