Congrats on the TDI! When it comes to tuning, If you plan on utilizing your local dealership I recommend getting a piggyback module as previously suggested by another member. The piggyback works by tricking the car's sensors into reading different values to adjust boost pressure etc. , it's not quite as refined or effective as a reflash, but your warranty will be safe and they tend to offer a nice bump in power too.

I also recommend getting Carista, it's an OBDII dongle that connects to their app and allows you to not only scan and clear fault codes but enable different factory settings on your car. For example, on my car I enabled gauge needle sweep on startup, windows roll up/down via remote, and Drive Select (I have an A4 which didn't come with that standard). Basically you can make a bunch of little tweaks that make the car a little more enjoyable and it has no effect on the car's warranty status, if you do some searching you can probably find a thread listing all the possible electronic tweaks you can make to your C7 A6.

Happy modding!