I've not started a tournament yet, but will figure out something hopefully - I'm more concerned for the moment in trying to make realistic races, but it's quite tricky with the rubber banding, as I'm sure you're well aware already! Still, it should quite easy to figure out a fun tournament format - I was actually planning to do every race as a different driver, and adjust the settings of each car prior to each race (like ballast etc.) to keep things tight, but at this rate I will be lucky to actually be able to do it.
Two reasons my grid doesn't have Garage59 at the moment - 1) I've only got 1 McLaren, as I figured out a 'realistic' mix of cars would have 4 Merc/AMG, 4 Audi, 3 Porsche, 3 BMW, 3 Lambos, 2 Ferraris and 1 McLaren, and Sky Tempesta were my choice for McLaren because I got a cap signed by the drivers at Spa for or my nephew
Oh to have the full grid of 50-70 cars, that would be amazing to see, but it would also make it even harder to replicate in GT7!