I get the impression it is best to lower 35mm at front with eibach springs and 35mm on the rear torsion bar. You wont have to have new alloys but it will look better!
Dunno how the Eibachs suit the original dampers but most cars with just spring upgrades feel like you are in a boat as the original dampers can't keep up with the new increased spring rate.
i think 4 Koni dampers will be about £400. Eibach springs are about £90 ish.
labour varies but i'd guess about £100...and you'll need the front tracking checking afterwards..
Eibachi springs
Rear torsion bar and GTI rear anti roll bars.
280 pounds fitted. Lowered by about 35mm and handles like a different car. Just make sure you have the rear end uprated in some way as just lowering it by adjusting the torsion bars will FCUK the handling (from what I understand). As Lyndon said try and talk to WEBCODE.
if you just fit uprated front springs the car will want to understeer more.
The rear end will suffer from the same body roll as before (regardless of uprated dampers) but the front will resist roll due to new stiffer springs.
This will in effect lift the inside front wheel losing front end grip.
Uprating dampers help resist initial turn in body roll but when settled into a corner it will roll as before.
having said that the slightly lower centre of gravity will help reduce body roll but this wont have as much of an effect as the stiffened springing.