I am now on my second C8 after two C7s and have no regrets from making the move. Maybe I have been fortunate but other than the software niggles, which largely seen to have been resolved on the latest cars, I have had no major issues with the car. That is not to say the first C8 was fault free, but then neither were either of the C7s. Nothing has happened that I felt could not have happened with any other make of car and my general position is that things can go wrong regardless of how much you pay for the car, what matters is how they are resolved and in that respect I have been fortunate to have great service from the same Audi dealer for nearly 25 years.
Both my C8s have been squeek free, although it is early days fro the latest one. I am perfectly happy with the touch screen and would say is it is a better implementation than one on my wife's Golf 8. What you may find a challenge is that to get options you would like you either have to buy bundled packages or go up a trim level, and then you get a lot of things you may not want as well. We have both WLTP and the UK tax system to thank for this and Audi is not alone, Mercedes now offers virtually no options other than paint colour on its cars. This is to ensure the customer understands fully at the time of purchase what the CO2 value of their specific car is and not have a shock when it is delivered that it is much higher and therefore more expensive to tax than anticipated and if a company car a higher BIK tax.
What you won't have access to of course is the BiTurbo diesel so if you wish to stick with diesel you will need to either go for the S6 or settle for the slightly less powerful 50TDi