We toured the GAP last summer, it was great fun. Here is a short journal, you can find others on the crazyguy site as well, do a search on GAP.
http://www.crazyguyonabike.com/doc/12687
As for food, take what you can get, there aren't a lot of options. The Whitehouse in Meyerdale was a decent place, we stayed @ the Levi Deal B&B, it was a good way to send the last night (west to east). The Trailside bar/restaurant/bike shop in West Newton was also decent which was a good thing because there isn't really any other choices. As for what to see, it depends on your interests, we added a detour (via car) on our way out to see the Paw Paw tunnel on the C&O. If you haven't been to Pittsburgh I'd add some time to check it out, we went in the day before our "start" so we could ride down to the point to say we covered the whole trail.
You didn't mention your lodging plans, the choices are also limited in the trail towns, plan on B&Bs or guest houses, Cumberland & Pitt have hotels. Oh and bring ear plugs the trains run 24/7.