The thing most people forget about german cars is that no matter how cheap they become Tom purchase the maintenance costs are just the same. So like you say, people just leave it if something big starts to fail.
Not necessarily as it depends on when the car wants to do a regeneration on the dpf.
Unfortunately dog and egr issues are common problems on most modern diesels these days. Use the search function to see the different threads to see what I mean
Yes you could end up with blocked dpf with soot if the engine isn't run hot for long enough. I'd definitely advise a petrol in your case.
Also I'm not sure what towns/cities you visit but diesel will be more of a problem if emissions zones are brought in.