To some extent, this varies by discipline. However, even in English (the least signpost-y field of all, I think), signposting is a good idea and a commonly accepted stylistic device.
I found that my high school teachers and undergrad profs all trained me gradually not to signpost, but then my grad profs trained me gradually to do it all over again. Now I find myself doing it more and more, especially in documents as long as the one you mention.
I would also say that signposting is extremely extremely helpful in early drafts, so I find that the most helpful thing to do is to signpost like mad and then, as you are doing final revisions, decide how much of the signposting to take out.
Chime!