C8 questions from a newbie

[X81]

Greetings, recently picked up a nearly new C8 40 A6 avant S and got a few questions that possibly this forum can shed some light on.

First one that i think isn't possible but it costs nothing to ask.  On higher spec models i noticed rear air con controls yet it seems this isn't std unlike the earlier A6's.  Wishful thinking i'm sure but does anyone know if you can simply source a controller and plug it in or if there is an installation kit?  It would be a lovely thing to add if it is possible.

Throttle response is pants, i've seen it mentioned as an issue but is there a fix from Audi?.  I'm in the dyno industry but through motorcycles so not averse to having it mapped however no one can tell me if the map will show in the ecu memory as a flash and void the warranty, anyone mapped their C8 yet?

lastly, it came with the std 19inch wheels which look ok but i was looking at fitting 21's.  Again has anyone done this and if they did was it a straight fit or did you need wheel spacers to keep the inside edge of the wheels away from suspension and calipers etc.  Research on this has been inconclusive so looking for real world feedback if possible.

Thanks everyone.😊