I've run a multi-round tournament at GenCon using RM so I have some relivant advice I suspect...
As others have said, you're probably best using pre-generated characters. Just make sure you have, we'll say, at least three choices for each player. You'll spend a LOT of time trying to explain and make characters and some of your players won't even care what system you're running, they are just there for the game/story.
Pester the hell out of ICE on the support topic. Meaning ask for help and if they say you can get it then stay on top of them. Make sure you get what are supposed to with enough time to use it. Nothing against them, but this isn't their primary job/source of income, so things can slip through the cracks.
Hopefully you got a hotel close to the center. Hauling around stuff is no fun. I will pay twice as much to be within walking distance to the center... after being 20mins away once I'll never do it again. If I can't afford to be that close I just won't go. But, I'm in Seattle, so going to GenCon is a 'big trip'. It's not like I'm just driving over from a state away or anything.
Bring hard candy or LOTS of liquids. If you are not used to talking a lot, and I mean a LOT, you may lose your voice. I ran four four hour events, not even on the same day, and my voice was about to go by the end.
Have extra dice, writing utensils, and notepads. Players will show up with nothing. Also expect no-shows and have a sign to put up that says you're looking for more players.
Find out who is going, get cell # for texting or email info, see what peoples schedules are like and try to arrange a dinner for when the most people are not gaming. Expect a no-show or two. Also expect them to bring along unexpected guests (not an issue so long as you are ready for it). You probably won't nail it down until a few days before the con. Find out if anyone has any diet restrictions then I'd recommend picking out a place close to the center. When we did it we went with St. Elmo's (that might be more expensive than some want to pay - but I always do one 'expensive' meal per GenCon, so that was it).