I wouldn’t necessarily consider the Audi to be a problem car at this point. Audis have known faults? So does every other car on the planet but brakes are a normal wear and tear item. Bad brakes does not mean the car is inferior.
Clogged sunroof drains often mean that someone was parking under trees that were shedding. Again, this does not mean the car it bad. That’s someone’s poor choice of a parking spot is all.
In theory the motor mount should not have failed at 50k miles and at a young age but parts do fail prematurely on every make of car out there.
The reason why many shops appear to be evasive to you is because it’s impossible to make a guess at the problem over the phone. I would also recommend that you do not adopt an attitude that a high price means you’re getting ripped off. A high end car often takes high end cash to fix and seeing as how this car is going on 7 years old that brings up the timing belt replacement issue, something that is not cheap either.