Welcome to the forum!
I can see that your post is quickly falling to the bottom.
First, I may not necessarily answer your questions, however if you can:
Check with local Porsche shops and ask your questions there. I am talking an independent good quality shop that you will be visiting once you buy your car. Remember, you are not a mechanic = you will need one, reputable and reliable, to do normal maintenance and repairs.
Get someone with Durametric software to check if engine was not over-revved, deviation on camshafts, etc. I am sure more knowledgeable folks would chime in on this subject.
Lastly if you see the previous owner’s eyes going glassy as you drive away, then you’ve got the right car.
Trust your instincts, I walked away from a number of transactions just cause the vibes weren’t right.
Make sure you have some funds set aside after you purchase your car. Trust me you will need it to fix everything that the previous owner neglected. Could it be a battery, tires, shocks, all filters, oil, brake fluid, I can go on and on….
Good luck and trust your own feelings.
Some links for your reading pleasure:
Engine failures:
http://www.total911.com/news/996-engine-failure-should-you-be-worried/
Mixed bag of opinions (as always on the net):
http://www.rennteam.com/forum/thread/295906/realiability_of_996/page1.html
Really decent article in PDF:
http://www.autofarm.co.uk/pdf/Total911_July06.pdf