I have a diesel and do 6 miles to work each day and do have long commutes etc. Never had any issue with the DPF as the mk3 manage it better than older models.
As you are looking at 3 years old then the timing belt and water pump won't need doing. However the pumps have been known to fail as there is a sticky on this forum you should read. If you go DSG make sure it has been serviced at 40,000 miles.
I enjoy mine and sometimes wish I had gone with the petrol 245. But then I dont when I get 600 miles + to a tank on very long commutes.
The FL diesel have the smaller 312mm brakes where as the PFL came with 340mm brakes. Either way they will stop as my mk2 VRS had std 312mm brakes and coped just fine with 280bhp!
Personally I would look for one with the winter pack, (heated front screen and seats) Canton Sound System, park pilot and Cruise control. Some come with ACC but I have had it on older cars and never used it.
You can activate features such as auto high beam,m and other features via VCDS or OBDELEVEN. I have the latter and it is worth its weight in gold.