Here's something that works very well for a such contest
You put on individual paper the name of all the games in one hat and you put the names of all the contestants on an other one.
An innocent hand pick up randomly a paper in the first hat in order to select a game, then 2 papers in the contestants ...and you have the first duel.
Repeat the operation for all the games/contestant and you got the first round. In that way only two persons will need to access one cabinet for their training session for let say 20 minutes (if needed of course).
All the winner names from this 'first duels' session go back into the hat, and the random pick up can continue...
I've done this in the past during an arcade meeting, and it was very fun... and for information, I was eliminated in the first round following a dual against a girl on ... Soul Calibur!
It's very fun because you don't know what will be the game you'll have to play, and so you must train yourself on a game you didn't played so far... Pressure Pressure!
Imagine Superully playing on a pinball machine, or André on Dragon's Lair... Damn! I want to see that