The Skinner book is excellent describing the terrain that can be expected but the description of the services is lacking, mainly because times just change. There is a 2004 edition of the book, but it is still out of date. I think the recent recession has made a big impact on being able to operate a seasonal business. The NPS has scaled back the operation of their facilities.
One thing I did was use Google's satellite view to scan the intersections to see if anything was actually at the intersection that could be useful and built a list. What you do not want to do is leave the parkway for a facility which is 3 miles away but 2000 feet lower in elevation. You will not be able to see any services from the intersections.
That being said I will say my big restocking points were the Wal-Mart at US 220 in Roanoke, the market at Meadows of Dan, VA, Food Lion grocery store in Blowing Rock, NC and the Ingles grocery store at US 70 in Asheville. All those places can be reached with no distance or elevation penalties to be incurred. By using those stores on BRP I did not really carry more than two days worth of food.
I probably ate my meals equally split between my camp cooking and restaurants. I would eat meals at a restaurant if it was convenient and just felt like it or would just eat out of my pannier or at the camp if not. I tend to prefer my own cooking rather than restaurant food, however it is hard to make everything when you have to eat so much to keep going.
The two times I have ridden the parkway it took me 9 days one time and 8 days the other. I rode the Skyline Drive in 3 days but have never ridden the whole route as one continuous ride. Be prepared for rain because it will, I usually ride it in summer because then the rain will be somewhat warm, in the spring or fall it can be very cold at the higher elevations. You can plan your travel schedule and you may be able to keep to it, or you may not. Fog and a cold rain can put stop to your day instantly.
NPS campgrounds are basic and lack any kind of services, but are beautiful. Private campgrounds have services but are pricy. Motels can go either way, the NPS Inns are very nice but not really luxurious, pricy and probably worth staying at one, but I would not stay at all of them. Certainly worth a meal if you are there at a meal time.
There is no way to prepare yourself for the hills, you just grind it out. You will spend all your day climbing. A mountain that takes 2 to 3 hours to climb will be descended in 20 minutes. Eventually you don't care.
It's as a nice of a place to tour as any place in the world. You will be glad that you did it. I think more people would do it if the logistics of getting to the ends wasn't so difficult. The difficulty of the terrain also discourages all but the most self-confident riders.
More specific questions might get a better answer than this so ask something else if you need to.