The first thing to do is to get the chassis refreshening as the car is a used one. You said you have tuned it already, I hope you haven't made the quite common mistake of increasing the rigidity before refreshening the chassis. If you did and saved the game, the handling of your car is gone for good and there is nothing you can do.
If you want it for racing use, Duck's settings are good indeed. They are quite easy to drive and produce very fast lap times.
But if there is something you don't like in those settings, I recommend getting Scaff's Tuning Guides and using them as a reference for making your own.
i agree with Greycap, hopefully you haven't fit the cage before the refreshening. and i can also recommend Scaffs Guides, although Duck has also good setups - look at his Tuning-Workshop for the setups.