I did this ride in Nov. and posted a bunch of info on this thread
. Scroll through it and you should find some of what you need.
Also, to answer your specific questions:
1. Generally good, they were redoing some spots when we went, so there was soft dirt. Also, it had rained a good bit the week before so there was mud and puddles in places. I was glad I ran fenders
2. I used an old road bike w/ 35mm tires (they actually measure 32mm) - works fine, but we were moving fast and hauling a lot of gear with tires pumped rock hard means you feel every pimple in the trail.
3. Best map is the one the Park service puts out. Another good source is a Boy Scout booklet on the Canal (184 miles of Adventure?), not sure where to get it, it was given to me as a gift.
4. Yes. Start in Cumberland and end in Georgetown.
5. Not really, but Bill's place at least had Yingling Porters and there is a good Pizza Place in Shepardstown, WV that has a few good taps (Hop Devil) and good pizza. The price on pitchers was pretty good.
6. See earlier thread. Make sure you follow the detour at Dam #4 (or was it #5?) - it's well marked and necessary. The detour at Great Falls is not necessary, but it was a bit tough portaging our loaded bikes over the rocky path. Worth it for the views alone though.
Have fun and take a camera.