Some of this is hearsay, but I have a theory on cracked windshields after "pro" installs.
I hear that the pro shops are required by law to use some kind of glue that is very strong. My theory is that when the windshield is held in with the glue, it can crack because of the flex of the windshield frame. My own suspension is very stiff and as I'm driving, I can see a little movement in the windshield frame so...
The butyl tape that was used when these cars were new might flex enough to prevent cracking.
Installing the windshield as VW/Porsche intended is very easy. I did it as a one man job. I suspect it would be best done as a two man job.
Remove the previous broken or cracked windshield.
Clean up the windshield 'bed.' I used a dremel with a abrasive wheel.
Mask and primer. Let dry and then ScotchBrite buff it to smooth it. Rattlecan spray to match.
You will need new clips for the trim, spacers, and butyl tape. These are available from AA and I suspect even George couldn't screw that up. The butyl tape is available from any auto body paint supply store. There is also a butyl primer that you put on the windshield edge before you set it. 914Rubber should put together a kit for this...
You put the butyl tape around the bed so that the holes for the clips are exposed.
Put the clips and spacers in place.
With a friend, walk the windshield over and set it on the butyl tape.
I happened to have a bunch of sandbags, so I tarped the windshield and weighted it with sandbags over night. But my understanding is that it sets when you put it in place.
Next day, I removed the sandbags and tarp and put the trim in place.
Things you might do while it's out?
I removed and replaced the forward dash vinyl and installed some tweeters.