General questions/purchasing advice A8

Hello, everybody.
As a long-time Audi Type44 driver and fan - currently in the 20V Turbo version - I look for alternatives/successful options to this vehicle.

For a few days now, the A8 has moved closer to the Visir - and I am now looking for information.
Since the searches etc have left a few questions open, I put the questions freely in the round:

The A8... is probably the most useful motorization as 4.2 (in relation to the still quite toxic 20V Turbo).

Maintenance:
Which consumptions expect a there - leading direction at Landstraße/Autobahn?

Tax: Euro2 - nothing better?

Insurance: Liability TK 23, UK TK40?

Motor technology
What about the engine itself - there were/are different revisions in the series - of which there are to be preferred ones?
Is the A8 V8 engine still completely based on the V8 (Type44) engine?



Transmission technology:
gear oil change seems to be mandatory (as much as I could read) despite the so-called continuous filling - are there any other special features to consider?

How old is such a transmission - as old as the car?

Technical General:
What are the "usual" errors of the A8's (except the front axle ;-)
Is targeted self-screwing (not rumbasteln!) still possible?

Yeah, that's the first questions...
Maybe someone can feed me some info?
Thank you!
Greeting Manfred