Good luck with organization even i don't think it will be funny as in native, i support you. I know there's just an idea but you've to start think about rules like how many rounds will be played, which items we can use or we can't use, what kind of builds we can do or we can't do.
I suggest you to do this tournament with skip the fun characters so amount of levels will be equal. Also match dates are so important thing because of strategus. Are you going to do like knock-out or league? League would be awesome because i knock-out system when you do mistake you're out, in league it's different you've chance to improve your tactics and learn from your mistakes etc. Also if you start to do this tournament a ''Nations Cup'' section in forum would be fine, for announcements, team informations etc. Since there's in-game money in this mod there might be in-game rewards for this from organizators or from devs (if they support).
I just suggest something because i think this would make this module much more funny for the players who like playing competitive, also i got experience about this kind of tournaments.