Well, i think original 550 rims won't fit 100% when it comes to colors, because the 550 Carrera GT silver is a little bit darker and tends to get more into a grey than the artic silver your car has.
But you can go with the Carrera style 18". Maybe you can paint them with polar silver and add some black to the paint to tone down.
I have the 18" Carrera rims with the red S calipers and i still like it. Also like the Techno wheels. Don't like the Turbo 1 and 2 wheels.
At the end of the day i everything is a matter of taste. And tatse can be very different.

I would only go with parts that came OEM from Porsche. So if your car would be mine i would replace the rear lights with the red and white ones my car has and also would replace the orange front side markes with clear ones.
Rims. Well i don't think the are ugly. An because they are 17" i think they offer more driving comfort - which is a good thing in my opinion. Maybe i yould paint them in dark grey, or black to get more contrast.
Regards from Germany
Markus