Use the GTR V-spec and tune it within the regulations (transmission and weight reductions), and buy the aerodynamic upgrades. With these upgrades it's quite easy to beat the Ford GT.
Used the 09 GT-R SpecV, Race suspension, FC Transmission and aero parts. Adjusted everything and set transmission to 168 I think. Mission accomplished.
NO, you get a base amount and then everytime you do better than the previous best you get the amount of money above what you won last time. I.e. you can only win a maximum of 300k from the event, if it takes you 1 time and finish first or 12 times and gain a position each time
I think what's important is to NOT change your oil. Otherwise you would have to buy another one to tune it to spec. My GTR V-Spec was 517HP with everything off. So I had to buy an '07 GTR. Right now its at 484HP though.
I managed to get 2nd overall on my second try, and this is with me spinning out on one lap, so there is much room for improvement.