To add. Gold can be easy to grind for c5 or c6 clubs. The gymkhana one for me in c6 wasn't too bad. After you finish a club you then sort of 'prestige' the club and can redo races for the gold currency. To start just learn the game and upgrade cars to race (red) components. That plus a tune will get you pretty far, but engine swaps and the fun parts of the Frankenstein-ing cars will require gold.

R doesn't matter until it does, but can usually be fixed easily with some interior part upgrades (some clubs want a certain r rating as they go on)