Hello & welcome,
As Gibby said, the insurance will the equivalent to the Third World Debt at your age, so think carefully before buying a GTI without getting quotes first! I fell foul of this whenI bought my Cabrio - the quotes I was getting, if I could find a company to insure me at all, made me feel a bit weak at the knees...

As an alternative why not look at getting a pukka non-GTI Mk1 and have a look at tricking out the car in the old-school-stock-retro-look? V. cool, v. classy and on a 1.1 or 1.3 the insurance will be peanuts. Possibly.
Good luck anyway.