If you are not planning a whirlwind tour, you have about 2800 miles to travel, and much to see at each stop. I think you need at least 2 nights in DC, 2 in Gettysburg, 2 in Boston, and 3 in Bah Hawbah. 2 weeks might be tight.
In Gettysburg, 1 whole day for a battlfield tour, another day for a tour of the town, the Cyclorama, and the new visitors center. Lots of good CGs there.
In WDC, park at a train station, take the train right to the Mall. The campground will help you out on where to go. KOA in Fredericksburg is superb!
In Maine, make sure you see Scoodic Point! Fantastic.
Have a grand time!