You can buy proper subframes for the mk3 golf These are adjustable sh helpful if you have different height drivers, they are not cheap though.
Obviously make sure you sort the safety stuff like brakes etc first.
Sort out some updated anti roll bars, eibach or similar and get your alignment sorted out. About 1.5 degrees of negative camber on the front, and a couple of minutes toe out on the front works very well and helps the turn in. A decent set of coil overs made a huge difference over the cheap ones I had fitted.
Loose as much weight out of the car as possible.
Drive it and have fun
Paul 86s2