As already Said. Don't worry about the engine as there's no point.
The most important modding for any mk3 is the stance and rims so buy some cheap coilovers and stick some decent wheels on it. Deeper the dish the better.
And lower it around the wheels.
Then the rest is all your own touches like indicators, splitter, rear lights, headlights. Go in eBay in the styling section and type in mk3 golf. Loads of diferant stuff on there mate. Always good to get bits that match each other.

hope that helps.