Thank you all for you replies! Much appreciated! I think that I got a better picture of what to look after.
My biggest dilemma is that it is hard to find high-mileage TSI's of newer generation. At the same time you can find many 1.6/2.0 TDI cars with many miles. For some reason I would feel more relaxed to buy an Octavia TDI with 100.000 miles, but maybe that has to do something with a positive public opinion of the reliability of the diesel engines. I also have to say that I own a 1.9 JTD Stilo Multiwagon with 170.000 miles on clock and as far as it comes to the engine I think that the car has a bright future ahead. Unfortunately I only make 5000 miles/year, so this is why I am looking into buying a TSI instead of a TDI. I hope that the TSI engine can reach 170.000 miles with the regular maintenance only.