I did the GAP in early September this year, camping. Pleasant high and low temperatures. No rain. No real bugs to mention. Started out from the Point on a Saturday. I didn't see too many people who looked like they were riding through. Of the few that did, all but one were heading north. Maybe kids being back in school had something to do with the apparent lack of through riders.. The owner of the guest house in Rockwood told me the place was totally vacant on the Sunday I stayed at his companion campground.
I drove out Friday and stayed at the Hampton Inn near the train station. Ran me around $200 for the night. I don't think they have an airport shuttle, but if you can get your own shuttle there, it's pretty close to the start.
I had originally planned to drive out Saturday and start Sunday, but I could not find an available hotel room in town for Saturday night. I think that was because of a U. Pitt football game and/or a Steelers home game. Something to consider if you go in the fall.