I just changed a set of brake pads on my friends 2016 TTS. We did not do rotors this time but were tempted to. The deciding factor is the thickness. You can measure that with a micrometer. The minimum thickness is stamped on the rotor. Nothing bad will happen if you go below the minimum thickness a bit but if you do so there will be a lip at the edge and that will cut into the wear sensor mounted on the right side caliper quicker than would happen with new rotors. This would give you a premature brake pad warning next time. The unfortunate thing on the Mk3 TTS is that it is difficult if not impossible to find an aftermarket front rotor for this Audi. This makes it necessary to buy OEM rotors from the dealership or from a dealership that does online sales.
on this car it is necessary to remove the Brembo caliper from the carrier in order to change the pads therefore changing rotors also does not add any significant additional labor. Oh almost forgot. We got pads on TireRack.com. Centric Posi Quiet Semi Metallic. I’ve used them on several cars. Very good pad. ( not for track use though)

Not too unusual. I wouldn’t worry unless one side on one wheel wore lots quicker.

True but the wear sensor leaves a good thickness when it wears through. 2-3mm I would say. You can see the outer pad thickness just by looking too. I always tie the sensors off and don’t replace them anyway. They are pricey and I have never had pad wear catch me by surprise anyway. Just have to pay attention. Sounds like you do.

A bit more than average but not extreme. They are not tapering end to end which they will do if you have a piston seizing. I would just keep an eye on it. Look thru the spokes at the pad thickness occasionally. When it gets down to 2 mm or so change them out. My friend and I do track events. We go thru them pretty quickly.