Hi Latte,
I can relate to the stage which you are in writing your chapter. I've been in similar situations for all my chapters I think, and I found the best way to tackle it is this...
First, don't worry about the length for now, but try to do your reading and looking up more sources now. Add these in to your already massive document! Once you are comfortable you have the all the information and sources you need in there, then it's time to start editting.
What I find helps at this point, is opening up a new blank document and having it side by side with the massive document. I then work through from the start, copying and pasting paragraphs/sections in one at a time and editting them as I go along. I find it much easier that way to tackle the large document, and its good to know everything in that document is already in editted form. In the original document, I usually end up with sections/paragraphs/sentences that I decided weren't good enough, but I keep them just in case I change my mind or need them later on!
I hope this makes sense and helps?! Good luck with your writing!