Wandering soul from St. Mary's City, MD on 8/1/2021 1:18:40 PM:
I did the GAP and C&O (Pitsburgh to DC) in one trip 3 years ago and averaged about 45 miles/day without exerting myself. I just finished the Erie canalway in early June from Buffalo to Albany (actually Colonie) and went 45-50/day, again without undue strain. My average speed was only about 9-10 mph. So, I believe that 50 miles/day at 12 mh is very doable for bikers in average or above average physical condition. BTW, I started the Erie canal trip the day after I turned 75. I assume you are younger than I therefore you have youth on your side.
Regarding the east-west-east question, I do not believe it makes much difference as the gradient change is very minimal (much less than the GAP!) While the prevailing wind is westerly, again it was not a significant factor in June. Therefore where you start should depends on the logistics of getting yourself and your bike to the starting and from the ending points.
I am a fellow Marylander around your neck of the woods. Feel free to shoot me additional questions: firstname.lastname@example.org