In career mode, you can only have 1 car.In customization mode, you can have as many cars as you want.
from car lot
You can't. You can only use cars customized with career to use them in career.
No you can't.
on some stages you are given cars to race in, your damage will be repaired for free and you will not be charged repair markers for totaling, if you 100% the level you can keep the car!!. i would advise reading the manual!
There is not one
you have to go to you reward cards and do what it says
you cant get it in career mode
beat the whole game
yes you can unlock the Audi r8 in career mode but the version of the game has to be the collectors edition as i had the normal version of the game and there was no Audi r8 to modify but then i got the collectors edition of the game. If you have got this version of the game, you will have to first finish the career mode and then finish all of the challenges in the challenge series then complete all of the reward cards. if you have done all of this then you would have unlocked the Audi r8 also you will have unlocked the Lamborghini murcielago lp640, BMW m3 gtr and the koeniggesegg ccx. these cars will all be in the car shops in career mode but you can only modify them from the rims,ride hieght,spoiler ( all body modifications have to be from the aftermarket section), paint job and rim paint and vinyls. if you are talking about the ps2 and xbox version this will work only in the my cars section at the main menu.
Progressing through career mode. It'll be one of the unlocks in the races in the "Stacked Deck" territory.
If you are on pc there are game saves for it but if you are on ps2 or whatever you can only get it for quick race.