All I can say is good luck. Do you really need 6 tvs? Will there really be 12+ people there? For every tv, 2-4 people can play and others will still watch/talk. I feel like 2-4 set ups would be fine and I'd think your school could supply the tvs with a deposit to cover possible damage. (most schools have CRTs anyways, maybe even a projector which would be cool.)
Enforcing BYOC would be best, your not going to find GCN controllers in bulk in any store. You'd be lucky to find a local classic games store that still has some in the box, you could order them from Nintendo, your better off your own and a few extra to share.
I'd say the best way to handle this is 3 full set ups. One for King of the TV where loser gets cycled for the next challenger, winner staying. One for 4 player FFA or teams and one for 1v1 sets, if people are waiting you switch after a set. More set ups is always great but if your buying the set ups rather than bringing your own it could get expensive and again, people will watch/talk and you should see how many people come before you go out and try to wrangle up 10 cubes.
Your best bet, bring your own set up, make people pay 5$ to join and use the money to buy yourself another one to bring which you can keep for tournies and finally, ask people to bring their own set ups. I've thought about doing this but I feel like it would always be the same 4 people coming to it plus some randoms and no one would care about improving so just a few set ups would be nice to attract people into the scene when they play you.