Imo, once you reach Delaware bay, it really doesn't matter prior to the 1st of the year. There really aren't magic dates before the 1st of the year. Go early and you may be dodging a hurricane. Go after hurricane season and it Northeasters may have you hiding for days.
While North of Norfolk you may have to look a little harder for marinas with water and pumpout services in late October, November, and December, finding marinas with bathhouse facilities isn't difficult.
I left in late January from the Crisfield, MD in 2016. Was able to fill the water tanks and use their bathhouse. It was miserable sleeping on the boat as the water was starting to freeze. Norfolk water temperature was over 10 degrees warmer and from that point cruising is reasonable.
Probably the bigger question is whether this trip is sightseeing or a delivery run? If you plan to stop along the way and sightsee, late September and October are very comfortable on the Chesapeake. I did this last fall and enjoyed several nice days at St Mary's city.
Ted