In reply to Heike:
Yes, book accomodation, especially in Fort William. The N3P groups will be in full swing at that time.
Having fixed accomodation in FW does complicate plans but accomodation is finite.
Walked the WHW in the 90's. I tried to book accomodation, for May, in the January. The solution that I came up with, as I was finding accomodation hard to find, was to guide the route for a company in return for free accomodation, in a B&B, for me and my OH.