As somebody who ALWAYS wants to organize tournaments for whatever (computer games, mini's games, sports I play, etc), let me share one important thought:

Get a firm commitment from the people you think want to play. Start with what you want to do, then gradually dial it back until you have commitment from enough people to do SOMETHING. Once you get them hooked, you can ramp up to more exciting stuff, but the key is to set the hook. Yes, have your big idea dream that you want to do, but expect to pare it back to something much smaller until you're established as "THE GUY who runs that GREAT tournament that everybody wants to participate in." Be patient, enjoy the learning process, and man, congratulations for having the balls to put yourself out there by trying to organize something like this!

Good luck to you!