1. Possibly, if you look at them side by side you'll see if they are different, the 50mm inlet bulges out whilst the 42mm is more straight.
2. Think 256mm brakes came in 89? Get your tape measure out

3. Pretty sure the gearboxes are the same
4. Shocks will be same as will front springs, but rear springs may differ as the jetta is prob a wee bit heavier at the back. But remember theres no telling what suspension setup they have on there now, who knows what previous owners have put on

5. Entirely your choice, my prefered option would be to fix the PAS kit

6. Differing oppinions on this one, think the popular suggestion is to fit KR cams into the 2.0 engine, but I've heard reports from 2.0 owners that it doesn't really make enough difference for the effort! Think its only worth doing if you get one of the de-tuned 2.0 16v motors, the MK3 ABF cams are fine but I think the Corrado ones are a bit weak.