A PPI is a must, consider it an insurance policy. I spent $900 on 3 failed PPI's before I purchased my 911. You making a smart move.
Another piece of advise.
I paid to have a PPI done on a 930 for sale here years ago. While it was int he shop getting the PPI done someone bought the car out from under me. They offered to pay for the PPI and then purchased the car. When it seemed to be taking a long time to get the PPI results I inquired with the shop and they referred me to the owner. He informed he he paid the PPI price himself and sold the car to someone else, never informing me what had happened. Poor form IMHO.
I would send a refundable deposit to the seller to show intent and to lock in your transaction to buy this car. This is what I did when I bought my 3.6 swap, I sent 2K to the seller with the understanding if the car failed the PPI I got the deposit back. Then the balance was wire transferred once I had the title in my hand.
Its the perfect time of year to fly to Detroit and drive the car back over a 3 day weekend. That is what I would do it will be the same cost as shipping the car and more fun.
Congrats!! I cannot wait to see this monster in person. When are we hitting a PCA AX?
Oh, and I think its impressive that a buyer was toiling over this Vs. a M5 what a compliment to this car.