I wasn’t trying to be negative, not really sure how you read that into it. Maybe you missed that I was also agreeing with you? Your “life experiences” are exactly my hesitation with an A8 and most builds on here.
And to be clear, the 6.4 reference is pertinent as the OP has that exact motor in his car.
Pretty cool to be called a youngster. While I’m not in my 70’s and certainly don’t have the wealth of experience you do, I’m pretty far from being a “youngster”.