Whatever braking system you take off the donnor car/ buying i.e Audi 80 coupe just quote the car when ordering parts so your discs will be 256mm 4x100 stud as you have four wheel bolts it will be 4x100. The other items you will need is a new set of brake pads, brake hoses and splash shields, ironically i'm selling the shields, which are for an Audi 80 disc size, as it will bolt pefectly to a MK1 golf hub.
The carrier all it does is correctly space out the distance from the hub to disc so you have a floating caliper on top to get the required clearance!
Just google MK1 front brake upgrades I'm sure there is loads as I did this back in 2000 so 12 years have gone by and its just standard to upgrade those MK1 brakes these days?