Ok I'm not going to be much help but here goes, I also have a 98 528i, mine is a standard and it has just under 80K right now though
1. Assuming nothing has been done except oil changes..Water pump, belts, gasket leaks etc.
2. ?? Ask the stealer...I mean dealer.
4. If it was me... new oil and filter, replace all air filters to include the wildly overpriced Hepa's, trans fluid, diffs, flush the brakes and replace pads if needed. I'm anal retentative though.....
5. my guess, 90K miles, not being driven over 70mph to much, oil maybe has not been changed as needed in the past.
6. How much money you got?? It likes everything and everything costs money...normally, generally, most of the time..lots of money.
8. Don't know
9. Yes E39