1.
https://www.panjo.com/buy/stock-exhaust-2012-porsche-cayman-s-987-2-75369
2. PIWIS but it is kinda pricy.
3. Unknown. Lifter noise, valve train...
4. Best way to check is on an alignment rack. Bent sway is unlikely.
5. Rear hatch should be true with even gaps all around. I never had to adjust mine but it is probably reasonably simple, just like a hood adjustment.