I did the pitts-dc a month or so ago… it was a really nice ride to cumberland on the GAP, but after that you run the C/O canal and it gets much rougher.
Here to ohiopyle wouldnt be bad at all… it would depend on how long you wanted to take doing it. It should be a fairly nice weekend ride. The elevation is mostly climbing out to ohiopyle, so your return would be much easier on the legs. I know I wasnt worried about my legs that much, but your butt is a different story. get the right saddle and you’ll be good… a pair of riding shorts/knickers/pants are also manditory. My buddy bought a 2nd pair in cumberland on our dc ride! Other than that, my knees were feeling it after the 200mi mark, but proper diet and stuff you’ll be fine.
Are the shorts really necessary? I usually ride about 14 to 20 miles and my old bike used to give me some pain but that was a mountain bike with no shocks and a crappy seat. Now I have this and the seat and front forks have shocks: