Ok, you will have a few items to replace. Plan on spending a few grand. Just do a search here and you will know what to look for. You made the right choice. I rented a Magnum once and though there was lots of hp, the workmanship was awful along with rear view etc. I also thought it wasn't too roomy for its exterior size. I have three to schlep around on wknds and the 525it is perfect. For driveability, I don't even realize its a wagon most of the time. Good luck with the fatherhood and the e39.
2002 525it / 172k mi.
02 525iT sport M pkg (187k mi)
09 328i convertible sport (50k mi)
12 Acura MDX advance