Original post by QHFIt sounds like you could benefit from talking to PhD students in your department. Also your university library will have a collection of previous students' PhD theses which you can access: call some literature ones up and see how they're structured and what they attempt to do. You could also see if the library has any books like Dunleavy's Authoring a PhD (which comes from a political science context, note) -- books like that are by no means cure-alls, but they might give you a better sense of the task.
I think 80K to 100K is pretty standard in the humanities, yes.
That's not a bad way of looking at it. In fact, one of the things that hinders some PhD students is that they get too idealistic about it: the thesis isn't meant to be your life's work or your finest achievement -- it's big, and it has to meet certain criteria, but once it meets those criteria you should finish it, like any other piece of assessment.
On the other hand another model for what the PhD thesis is is the academic monograph: a thesis is a bit like the first draft of a monograph. The relationship between theses and monographs is a bit like the relationship between long master's essays and journal articles.
So perhaps it's good to think of the thesis as something between the two poles of 'just a mindblowingly long essay' and 'an academic monograph'.
You break it down into small achievable chunks and do the chunks, one by one! The exact way that you work with your supervisor (or supervisors -- some people have two) is a product of negotiation between what you think you need and what your supervisor thinks you need, but most people are writing draft sections which they then submit to their supervisor, who will add comments and suggestions (but not a numerical mark). During my thesis, I ranged from times when my supervisor would send me off for two months to clear the ground and bash out a big chapter draft to times when I would be redrafting something and getting comments on it about once every week, depending on the phase of the work I was in.
Most departments also have more formal internal checkpoint/annual review systems, so you're likely to have to submit draft sections for review by other scholars two or three times during the process -- this is so that the department know you're progressing and to catch any potential problems which have slipped past your supervisor.
Believe it or not, most people find at the end that they have too much material, not too little. If you work steadily at it it takes surprisingly little time to write a PhD thesis. Which is good, because if you want to have any slim chance of an academic job afterwards you need to be filling out your CV by doing a range of other things: publishing, teaching, going to conferences, helping organise conferences, applying for grants for side projects, &c. (If you're not hoping to roll the dice on a career in academia, you can be much more relaxed about these things.)
I kind of do mind, because talking about that publicly would make me too identifiable. I suppose I can say that I work in English, on English which is earlier rather than later. I submitted the completed thesis late last year and that I did enjoy it, though it was very hard work. And don't worry about asking questions, I don't mind that.