I glad to hear you say that Gavin because I am expecting my first at the end of the year!
Welcome to the club Mike. All the advice given above is good. When I was looking for mine at the end of last year I memorised the buyers guide and did everything it told me to do. Its an extremely well written guide and will p**s off the seller when you are doing test number 416 but honestly its far better to do it. I use mine as a daily driver and its brilliant. Comfortable and refined around town and an animal when you want to open it up on a sunday afternoon. I would suggest going for a 3KGT over a GTO but I have never owned a GTO so I can’t put up much of an argument for it. Other than you are more likely to get a lot of history. I would suggest buying through the club if you can. The cars will be known by members on here and there will often be a build thread you can read through.
If not through the club then make sure you get a lot of history. And I would save buying a cheap one to fix up for your second GT/GTO once you know your way around it better!
Good luck on the hunt dude and get some pics up when you have your girl!