welcome.. can only help with a few mate

telling if its a 8v or 16v.
1) it will say its a 16v on the v5.
2) the 16v has 16v in big letters on the engine (look in my gallery)
3) theres a sticker in the boot (see my gallery again) that'll say 16v if it is one.
4) visually it should have a lil red "16v" badge under the GTI badge on the rear.. plus.. a red 16v badge on the front. generally the GTI has that huge ugly silver GTI badge onthe front. mostly thats enough to tell, but i've seen valvers with just the GTI badge on, or even with the silver GTI badge AND the red 16v badge on the front. (think someone once said earlier valvers may have come like that)
if its got abs there is an indicator to the right of the steering wheel, if you have airbags the indicator for that is also there. both should come on when you start the car, and go off after about 3 seconds.
i'm not sure if the 8v had brake wear indicators. the vr6 and 16v do.
