I've been to GenCon a few times (in Milwaukee). I ran a multi-round tournament using RM many years ago and actually had some fun doing it. I was worried it would be more work than it was. Personally I'd recommend running your event after the merchant hall has closed. There will be more people available to join your event and it will leave you with time to check out the merchant hall yourself and play in other events during the day yourself.
Put simply my event was a "no-rules" chariot race. You picked from some pre-gen characters then selected your chariot (speed, light, med, heavy, war). I wrote up some critical charts for chariot-to-chariot collisions. There were two 1st Round races on Friday and Saturday and a final 2nd Round on Sunday. I took the top three racers from each of the first rounds for the final. You earned points for kills and placement. Medals were 1st, 2nd, 3rd, Most Points and Most Spectacular Death.
I've been wanting to go again, but this year is almost surely out as my wedding is set for Aug 25th.
The only downside for GenCon is it pretty much ruins all other Cons for you.