your car should have an iso connector that will plug straight in. (you may need to swap yellow and red tho)
no the original vw connector should plug straight into the pioneer block (mine did), so no chopping wires etc and you just need to unplug the pioneer lead should you change it ever
if you use std car connector to pioneer connector no wires need to be cut...and should you ever change head unit again its a simple unplug job
at worst you will need a coverter lead, available from maplins or halfrauds