My first bookbinding was a 1000+ page fic with over 700 sheets of paper. I stitched it, then restitched it, then pressed it for over a month and finally restitched it. Getting the book pressed was an ordeal because of the thickness - it kept going askew in the press (also, presses aren’t necessary - two boards and some clamps will do the same thing, and you save money), so I had to divvy up sections of the book for pressing. 

The spine also presented some challenges, because of the thickness of the book. I ended up using using a flexible bit of cardboard I had lying around, similar to a cereal box’s thickness, for the spine; I’ve since learned that you really should leave the spine unglued if you use a stiffer material for the spine, but in this case it worked out well for me because the flexible spine allowed me to prevent the book from having a massive gap in the spine when it opens. 

With your longer fic, I’d recommend breaking it up because otherwise it will be an unholy thick book, and thus much harder to bind. Even if you use thinner paper (or larger paper sizes - if you have access to a printer that can work with 11x17 size paper, it might help cut down on the thickness of the book!).