This is where documented maintenance records from the previous owner is of high value. Without knowing how it's been maintained it could either be in great shape OR it could be ready for the trash bin.
If there's no records then I'd first rule out the big stuff. I'd want a compression test done: if there's poor compression you're going to be running around chasing your tail, big time.
Transmission, automatic or manual? If automatic then tick, tick, tick...
Assuming that the compression shows to be OK then, if no proof of it being done within interval (100k miles or within the past 5 - 7 years), do the timing belt.
There's suspension. Brakes.
If you can locate a TDI guru close by I'd consult with him/her (are there any "her" TDI gurus?).
How one approaches this depends greatly on whether one is expecting a reliable commuter right from the start or whether it's considered a project car. My cars have tended to be a combination, the amount of work has been like a hobby, though the intended use/goal has been to achieve reliable commuting vehicles (after 3 years I'm finally there! [this has been with two cars]).
Don't be surprised to find that this car is going to require $1k to $3k to get it safe and reliable.