Direction is a matter of opion. I like going toward DC for a couple of reasons. First it is downhill from my house to the start of the Montour which connects to the GAP.
Also it is a fairly steep ride up from Cumberland to the Big Savage. While others find the long steady gind up the the continental divide annoying.
I have never had issues on the Capital Limited. I will be using it again in September.
I hope you are camping or already have your reservations for rooms. July 4 is bound to be busy.
I would offer to help at the Pittsburgh end but plans, for July 4, are to be touring in Oregon.