I'm sure Spidey will confirm this, but I highly doubt there's any kind of limit on words or characters for front page articles. I've submitted some pretty lengthy pieces myself, although I wouldn't suspect much went over 20k characters. But I remember some of Notepad's old fictional pieces being quite lengthy and I'm sure some of those hovered around the 50k mark. However, despite my doubts about a set limit on words or characters, I'd recommend that you break your diary into a couple pieces and submit them separately.