Welcome Casey!!
I agree about the prizes! If you're going to give them out, I think it has to be to everyone that finished the game session (not counting if their character got killed off due to bad dice rolls or whatever), and contributed as a character to the fun. Picking out a best player can be done, but it's always painful to do. And for brand new players trying it for the first time? Cruelty!
(Having done some RPGs and LARPs at Conventions and been selected for awards for few times, I always felt uncomfortable because others had done good jobs in role playing too.)
As for gaming, there should be different games set up for levels of experience. And the description for the session should describe what kind of player is needed: beginner, intermediate, advanced. (And which set of rules/edition is being used.) That way, someone who is advanced knows if they are getting into a game with beginners, and they might choose to do so to help out or something. But at least they won't get peeved off while basic game play is being explained.
Or due to the unknowns on the numbers of role players, you might want to set up just two kinds of levels, beginner and experienced? Clearly the storyline for a beginner game needs to be a lot simpler and shorter to solve, because there's going to be more time spent on explanations than gaming at times. An advanced game would have a more complicated story to keep those players interested. Getting games finished on time with a real feeling of satisfaction from the players on the outcome, is a talent the DMs/storytellers must have, and at a convention is important due to schedules of things people want to do.
It doesn't hurt if the game session description includes something about "rules will be stressed", or miniatures rules, or "role play will be stressed over rules". There are different styles of gaming out there. Some people love the detailed rules and math game, some want to just role play.
And anyone interested in gaming really should go check out "DM of the Rings" online--it's hilarious and lays open a lot of gaming quirks that could help improve anyone's campaign, or at least have you laughing because your group has done the same thing.
Lastly, as for game scheduling, make sure you don't set them up during any possible important guest panels.
