no need for medium tires, super soft in front and soft in rear works just fine. You'll probably pit every 13-14 laps depending on how much you slide around the rear of the car.
The endurance races are pretty damn easy, if you run a car similar to the cars you'll be racing agaist (NSX's like Mugen, Raybrig, Mobil, ect...Oreca Viper, GT-One, 300ZX-GTS, ect...) you'll end up lapping the the entire feild between 3 & 9 times. The prize cars in the Laguna Seca race are nice too, you'll either get a 3000GT LM (Baby blue or pearl white), or the Rally Celica (AWD w/same paint as the Castrol Supra). Cross your fingers for the pearl white 3000GT LM, really nice car.