The following cheat will unlock the cars for you to buy so make a new profile under the name off: nOsLiW (the O is the letter not the number)

The next cheat will max out your credits so make a new profile under the name off: tEAm4za

I would use the money cheat to start off a new game with, sadly there is no way that I know off that will alow you to have both cars and max money on the same profile.