I did something similar when I needed to write a lot of fiction, except that my solution was a monstrosity hacked together from emacs, LaTeX's memoir package, org-mode, and a couple of Python scripts to convert from my own text-based format to TeX, and handle daily word count goals. It works great, despite being hideously ugly. And it was fun.

The Bean guy is right that it can be rewarding to make a word processor that works exactly the way you think. Even if it's not strictly necessary.