A fic this long doesn't get written (at least, not by me), without a lot of different sources for research, and a lot of discussion and beta help.
Main research sources (as well as LoTR itself, obviously) included:
The Silmarillion and the Unfinished Tales, the latter particularly for discussion of the history of the Silvan Elves and for the Battles of the Fords of Isen.
Barbara Strachey's Journeys of Frodo (Ballantine, 1981) for its detailed maps and commentary.
The HASA Resources section, which saved me from having to go and comb through HoME and the LoTR Appendices numerous times - thank you to all its contributors.
The Encyclopedia of Arda for numerous quick fact-checks, maps and its calendar converter.
Hisweloke (the Sindarin Dictionary Project) and Ardalambion for help with Sindarin vocabulary and grammar respectively, plus the Sindarin Names Generator and Male and Female Anglo-Saxon Names sites.
The wonderful Middle-earth Travel Times page was invaluable numerous times for ensuring I wasn't indulging in Peter Jackson-style Magic!Distance and was making my characters take an appropriate number of days to cover the miles.
Discussion and speculation:
I've pestered the Henneth-Annun mailing list with everything from the logistics of crossing the High Pass in early spring with horses to likely casualties from the Black Gate, and a thousand details in between, and can't thank my fellow Henneth-Annuniacs enough for their willingness to pitch in, research and discuss.
Since a number of chapters turned on dealing with horses and their behaviour, I was particularly grateful for the help of, at various stages, Sulriel, Erin, Karri, Jillan and LoH on those aspects.
Beta, comments and support:
Heartfelt thanks to: Forodwaith, Anglachel, Firerose and LoTR_lover for encouragement in the early stages, and Alon for beta-ing several of the early chapters (and Maia for later beta of the reworked versions); Drummerwench, rinlossien, curiouswombat and Erulisse for reading and commenting later on; and above all, Altariel and Julie, who read, gave concrit and supported from the beginning all the way to the end.