For beginning racers I suggest a car that is easy to drive. Make the front end push a bit so the rear stays hooked up. Dial out steering so the car is not so responsive, then go make laps and get super consistent. Once you are able to consistently drive the "safe" car, then start freeing up the rear of the car. You want the rear of the car to rotate enough that you can get on it around the apex of the corner without washing out or traction rolling. You will notice that the fast guys are fast because they can get on the throttle sooner in the corners than the guys who have to wait for their car to finish the corner. Giving your car to an experienced racer will just tell that racer how it is for him, he may think it is too stuck, yet be too loose for a beginner.
And yes, you should probably start at the stock setup and adjust from there.