If you would consider "used" wheels there are several reputable vendors that work with the PCA that specialize in wheels with perfect fitments for Porsche like BBS, Champion and others. I'm on vacation with family in NY and don't have any copies of Panorama near me but I think one of the bigger vendors is WheelEnhancement.com
Good luck and again, congrat's on the purchase. Many happy, safe miles.
I would avoid Champion wheels which are OK with very crappy finishes. All the paint will peel hence the bad resale value. A nice set of Volk TE37s would be the lightest and strongest wheels available for the 997 in the market, IMO. Tirerack is closing out the 18 inchers.
Steve