Hello David
Good luck with the FCP and do let us know how you get on. Don't underestimate the travel time between and within Orkney and Shetland, BTW, and if short of time my advice would be to choose one rather than try to squeeze in both. Shetland is a large, far-flung archipelago with ferry connections among its islands and loads of good walking, wildlife and scenery. Its Tourist Info Centre is very helpful. Can't speak for Orkney, haven't been (yet).
For planning purposes, on those long winter evenings, I'd recommend Lonely Planet's
Walking in Scotland. It's available very cheaply on Amazon.com (though sadly not in its 2nd edition, for which you would need Amazon.co.uk, ISBN is 1741042038). It includes the whole of Scotland, obviously and has material on the FCP and other long walks, and also valuable info on walking in Orkney, Shetland and much more besides. If you plan to visit Scotland in future, you may find it a great one-stop shop for information.
The FCP guidebook I have seen (not ours, but it looks good) is
Along The Fife Coastal Path (from Mercat Press/Birlinn) by Hamish Brown (who lives in Fife and has a high reputation as an author). I say this not to undermine the online book that bsmyth has pointed you toward (which I've never seen) but as another option which is available through Amazon.com marketplace (search by ISBN is fastest: 1841830577).
Delighted to hear that our WHW guidebook survived your challenging weather. Maybe we ought to consider doing one on the FCP? So far, I've been thinking that Hamish Brown probably did so good a job that there's no need. Please let us know what you think?
Glad that your attitude to Scottish weather is robust. We needed attitude to get through the summer we've just had

- although I've personally had some great walking this year!
Please keep us posted on your experiences and thanks for posting!
Jacquetta