We usually leave W. PA the last week of Jan. The rig is winterized and stays winterized through our entire trip, which usually ends in March. We don't de-winterize until May at home. We carry bottled water for our coach needs (coffee and cooking), and will use campground water when south for other needs. We use rest stops for BR needs as much as possible on the way south, but if we need to use the toilet in the RV, we add RV anti-freeze to the flush. Once south, we do not hook-up to water, but use campground water in bottles to flush the toilet, and obviously dump before heading north.
For the actual trip, consider not making reservations for the first few days of your trip. You may need flexibility on your leaving date due to the weather. Last year we had to delay leaving for two days because of weather, not at home, but in the states we would be traveling through. So, have approximate dates planned, but go when the weather is OK. You don't want to drive in ice or snow if it can be avoided.
Finally, remember that you can still get freezing temps and infrequent snow even in Florida, usually north of I4. A couple of winters ago, we had 34 degree overnight temps. in the Orlando area.