From DB to Audi: Again a purchase advice.

Dear Audi drivers. After 430,000 kilometers in my 500 SEL I want to switch to an A8.
In my eye I have a 3.3 TDI.
<100,000 km
25-30' €
1. Hand

1) What special equipment should I pay attention to (I like it "full")

2) Does the year of construction play any role in the 3.3 TDI? So during the short construction period, there was any facelift or engine change?

3) Is the 3.3 TDI really as vulnerable as many say?

4) What about chip tuning at 3.3?

I drive more than 30,000 km a year. The diesel comes cheaper...

Thank you very much.

Hans