If you will be driving the Lotus at high speeds, you'll probably want a downforce of around 15 / 30 (Front / Rear). That's all you'll need to settle the car. You don't have to do much (or anything) with the suspension since this is already the world's best handling production sports car, and the GT4 version properly reflects this.
If you're having trouble spinning at lower speeds, then my guess would be that you simply need to practice with it a bit more.
Good luck, it is one hell of a gripper, tight tight tight cornering, plus you can get the tail out when you want! Probably the overall best balanced car in the game.