I would recommend taking with you this book, which has detailed descriptions, and gives the name and phone number of every place to eat, drink and stay along the way, and also the official National Trail guide (by Burton), which is particularly good for its OS maps. A perfect book would combine these features.
On the walk itself, the first day (through central Newcastle), and the last two days (through Carlisle and to the sea) - were not the best bits: no visible Wall at all, and only the occasional sign of its accompanying earthworks.
If you plan to do it, but don't want to do the whole lot, you'll probably want to do the best bit, and this, without any doubt, is the central section: lots of visible Wall and lots of scenic (and hilly!) countryside. Not many shops or pubs, though, so you'll need to stock up on food and water. You can do this bit in a long weekend.
So, for a three day trip: (1) Chollerford (best campsite ever, and various inns) to Twice Brewed, (2) Twice Brewed to Greenhead and (3) Greenhead to Walton.
However, its is very satisfying doing it from end to end, and I would recommend that - we did it in eight days, which is slow - one group we saw did it in four (which is fast).