$4,500 is a good price.
Questions:
Weak points on the model? http://www.bmwe34.net/e34main/troubl...will_break.htm
What is reasonable trans life? until it fails. (no solid guess here, mines got 170k no problems yet)
What is reasonable engine life? +/- 300k.
Is there a recommended timing chain replacement interval? Never.
Can I assume that with the smooth idle and 163k the Nikasil issue is a non-issue? Never assume anything with Nikasil, if it lasted to 100k it may last forever, some say it is inevitable but so is any kind of engine failure above 100k. I have 170k some have more with no problems, a lot of nikasil replacements were also due to other factors and not necessarilay the engine block material.
How can I check trans fluid condition? Pop it up on ramps, jack the back up so the car is level. Must be warm to the touch (trans pan...not scorching hot not cold) remove recessed hex plug. If it drips out its good, if theres nothing coming out add.
Also, I plan on maintaining/repairing this thing on my own. I've got 2 Mercedes diesels (a '91 and '84) and have done full front end rebuild and timing chain on the '84 and all other regular maintenance on both cars. But, being unfamiliar with BMW and the 3.0 gas engine I'm a little nervous. The only fear is fear itself.
Good luck!