Not really a guide but more of an advice:
Each car with its separate tuning kits grants you the possibility to earn individual gold medals per tuning kit.
So, get used to a car and a track to earn some money to buy tuning kits (and cars/tracks obviously).
Once you know a track and earned a gold medal just switch to a different tuning kit, and getting another gold medal on that same track should be a breeze.
Repeating this method with the first tracks and just switching cars and their tuning kits might save you from buying the later tracks (though progressing to these is needed and more powerful cars will of course net you higher drift points and more money).
Hope this helps!