Enjoy the car and don't worry about the minor niggles! I bought mine from MacKay Trading as well - they treated me well even though I could have got the car a bit cheaper if I had been prepared to either a) travel a long way south to buy it or import it myself.
Mine has an after market head unit which I've left in because it's pretty good - the satnav doesn't work of course, and I have tried unsuccesfully to get a disk for it for the UK from Clarion, so I've given up. It plays NTSC DVDs, CDs, Minidisks and the Tuner works fine with the band expander that Mackays installed so I'm happy with it. I think they got this work done at Skidz in Falkirk.
The only thing that I regret is that I did not join this forum until after I had bought the Z. The stuff that I have learned from these guys is incredible! If I had known about the speed limit defencer, for example, I would have insisted that they installed that before I took delivery.
I'll look out for you on the roads. Watch out for the cameras!