1) Replace all of it
2) When in doubt replace it
3) Replace the trim you can't see (especially all window squeegees and felt)
4) Some of the trim is cheap some is incredibly overpriced (don't skimp on window seals)
5) Give yourself three times the amount of time you think it will take
Enjoy the ride.
Here's what the process looks like;
http://forums.pelicanparts.com/porsche-911-technical-forum/634750-just-became-porsche-owner-so-ive-got-some-questions-4.html