Just sniff around GTP and somewhere there is a step by step guide of how to progress as quickly as possible.
I just got an MX-5, did the first two races in the beginner league and just kept shoving bits on it. When the car finished enter the other applicable races. Keep making money. With enough cash, flogged it, then got an FTO GP-R, VR-4 Turbo then my Mustang.
After that it was just a question of buying the correct car for each race and tuning them right. Plus dont enter a race unless you KNOW you can win. Otherwise you'll ruin your win %. Mines only 87% due to an infuriating MR2 in some beginner race...............Good Luck
There is a GT3 Settings & Tuning Guide at the top of this board. In there is a good tuning guide, and if you search for the name of the car you want (and restrict it to this board) you may find specific settings.
Otherwise people usually go to www.gtvault.com . Here at GTP we don't maintain an actual settings databse because we've found that "off the shelf" settings rarely translate well to another driver.