Welcome to the forum.
There are a few of these doing the rounds. Here is the link to the most recent and most comprehensive list of things to check for when buying second hand and on delivery:
http://www.golfgtiforum.co.uk/index.php?topic=64432.0Many of the problems with the GTi were solved after 06 so your should not cause any issues.
Steel Grey is a great colour as it hides swirls, and dirt very well. Xenons is a must in my opinion and the Monza's are good.
With regards to monza's you may want to check for "White Worm" on them which will mean a replacement of all four rims for free warranty or not.
Certain engine builds had an issue with a fuel something or other. I cant remember but that you can check on delivery and will be fixed under warranty.
Before buying a second hand motor I would suggest getting VW to bring up the cars history. That way you can find out what has been done to the car, is it an import? Has the car had any major issues etc before buying the car. An example of this is Phil who almost bought an Edition 30 but after checking with VW found that the car was a lemon.
Other than that, push hard for a discount and only accept the car if you are absolutely happy with it.
Im sure I forgot a few things but others can fill in for me.
Happy Driving
