As someone who owns precisely what you're looking for, I can tell you some of the issues you'll run into and want to look out for at that age, though most of it is typical for any car of the same time period:
- Timing chain rattle. Unlikely, but it's possible.
- EGR issues. DPF is usually solid, but the EGR cooler can get gummed up and throw a code. There's also a point in the intake manifold that gums up and throws a similar EGR code, it'll have your local mechanic scratching his head forever figuring that one out... guess how I know.
- Despite saying the DPF is usually solid, you'll want to use something to scan the DPF ash level. Not only will this help you avoid one with a doomed DPF, it'll also give you a clue to if the previous owner serviced regularly with good oil. Bad/off-spec oil will prematurely raise the ash level in a DPF.
- Wheel bearing hum
- Brake caliper boots torn/worn
- Suspension bushings rotted, front in particular is often guilty of this
- Would be wise to consider replacing the water pump around this time
As long and potentially scary that list is, honestly they're pretty solid. Nothing on there is a huge issue, except for the timing chain rattle; if you hear that, run! It's all pretty standard stuff.
In summary - Get a OBD reader and the VAG DPF app, make sure that looks healthy. Scan for codes (Carista is good for this, can get the deeper more hidden codes most bluetooth dongles/apps can't find) Otherwise pretty much just regular used car stuff.
