A quick tip that I think it's worth raising, as it's just come to the fore in my life(!), is that the citation style you employ can have a large impact on the number of words over the course of an 80,000 word thesis.
I have been using, until today, the Chicago style with a full note on every page. Thankfully, I use Zotero, so I am easily able to switch the style throughout my whole document, albeit not so easily to an autor-date mode from a footnote. When I switched, though, to Chicago with an abbreviated note, I shaved a good 4000 words off my thesis; 4000 words that I would otherwise have had to lose from the body text.
In short: watch out for styles that overly repeat your bibliography.
Featured image by semuthutan under a CC-BY-NC-SA license.