The trick for me is to get as much stuff that can be used on both cars. This will mainly be Wheels and tires. This will also likely be the order that I begin purchases.
For both cars, I'll likely be trying to run either 17x10 or 18x10 wheels.
Probably hit the easy button here and order these from Vorshlag.com
Tires will be R-comp 295/40-17, 295/30-18, or 305/30-18 Kumho V710, or Hoosier depending on availability.
Tire Rack will get this order.
This will probably not be something that will be swappable.
I may just use the Koni's already on the 328, and add the Bavarian Auto (hard) springs that I already have.
For the Z-3, I expect to spend some cash:
TC Kline Racing Double Adjustable kit:
Forged Narrow Superlite 6R Big Brake Front Brake Kit (Hat)