Great pics! Love the Aero sideskirts. Are you still running the oem wheels? If not what did you get?
The original wheels are 18" - here's a picture:

Also, Ginz are you still on zpost? Some Z4 owners there are trying to do a Chicago meet, following on from a thread YOU started. I pm'ed you there.
The new ones in the top pictures are authentic M3 CSL wheels purchased via eBay.uk, they run about $1000 more than the almost identical Competition Package wheels, but are .5" wider up front. Total overkill on my part, in hindsight - if I were to do it again, I'd get the ZCPs and save the money (they were $600 to ship!). By the end of next week, I hope to complete my last mod - 3.91 gears in the rear diff.