Cedar, like you, I was very specific on the list of equipment I wanted for the Z4 (Alpine White or Space Grey, Coral Red, <15k, premium pkg, sport pkg). Actually not even as specific as you as idrive and comfort access weren't hard requirements, and it still took me a long time to find one that fit all of my criteria. So I know how you feel. There is always a risk with buying ANY used cars. The key is to minimize that risk and have a backup plan. If you really like this car, here's what I would do:
1. Get a CarFax (which you've already done)
2. Ask for a lot of high resolution photos in as many angles as possible of the exterior and interior
3. Get an independent inspection
4. Put your deposit on a credit card, so if there is any dispute, you can file a charge back with your credit card company and get your deposit back
5. Get someone in the area to check it out for you. Let them know your areas of concern so they can spend more time looking at those areas.
6. Know your rights (lemon law and warranty)
I've successfully purchased both BMWs in my signature remotely. That is, I put down a deposit before seeing the car physically in person. I flew in for one, and drove several hours for the other. Both worked out just fine. Ultimately you have to weigh the risk vs reward in any purchase. But we are here to help
