Nice work on the C4S! What year is is and how many miles?
Porsche paint can be very soft as you may have found out.
Great job on the interior and seats. I have the Adaptive Sport Seats which on the drivers side seat area, the leather is "puckering". Porsche rep did not approve replacement, which I now have to escalate up the Porsche command to have it done.
Leather in these cars have a very unique odor more so than other leather. Trying to replicate it is difficult at best, but a few product work well with it. One being Sonus, another being 1Z Lederfledge and Zaino Z-10. Sonus seems to be the closest I've found so far.
If he's storing it for winter, hopefully he will increase the air pressure in the tires to 60lbs and or use Tire Cradles. And use some gas conditioner as well. Obviously a battery maintainer.
For paint, I've found mild polishes and pads work best. I still use
Menzerna P085RD for most of the work. Any good sealant works well for winter storage. A cover wouldn't hurt as well.
Once again, great job!
Deanski