Warranty vs no warranty depends on what you can do with wrenches under the hood as well as what you plan for the car. If you can do your own work then it’s debatable on actually needing a warranty. If you plan to tune the car then you need to find a warranty that allows for tuning. Audi warranty will void a warranty if they find the tune in the computer.

Big tickets on the 4.0 platform are turbos, DSG trans, and the air suspension components. PCV can be a problem but Audi has extended the warranty on some years.

I don’t have insights past that as I have an A7 out of warranty and turn my own wrenches.