The word count for the Chairman's essay is 10,000 characters, so that's probably what you want to shoot for.
If you go to this page:
http://www.team2834.com/rookie_all_star_award.html there is a link to team 2834's Rookie All Star Award Submission. The judges will do their best to read it all, so you don't want to include too much "fluff" and you don't want to make it excruciatingly long and drawn out.
Good Luck!