When the hell did you get a GTI?
Yeah, the turbo and manifold will fit but since you have to flip the manifold and turbo to make them fit you'll have to make your own downpipe. If you don't flip them it wont clear the intake manifold.
The turbo on the turbo diesel it fairly small so don't expect gobs of power, but do expect lots of bottom end and fast spool-up time. I'm not sure what it will run for boost, but with a boost controller it's adjustable.
You need an intercooler on anything making more than 6psi... period.
Your compression is perfect. 8.5:1. It will take 20psi if you want, but I wouldn't do it every day. Those bottom ends are tanks.
There are a few ways to keep up on the fuel side of things. Check out
http://home.comcast.net/~vwmikelvw/ and go to tech. E-mail him if you want... tell him I sent you. You know his car.