I've got no suggestions yet for Pennsylvania, as I've not been there yet. If I come up with any, I'll drop my ideas here. I do like this website http://www.cnyhiking.com/ATinPennsylvania.htm for information, as well as the whiteblaze forum. You can do all of Maryland in 3 days (some do it in 24 hours). Harpers Ferry is fun and moving north, the terrain is very easy and the shelters are closely spaced along the way....parking is easy too.