Buy mine its for sale its so much cheapiar than starting from scratch trust me ... Just a quick guide your need a engine i went for a agu engine code as its got a bigger port head than a aum .. Your need
Engine
Down pipe ,custom exhaust
Gearbox clutch flywheel starter motor .. Ive gone full hog mk3 gti 16v drive with cable change
New mounts engine gearbox , rear mount
I needed my existing car loom sorted out due to all corroded wires
The engines ecu decoded
Loom of engine you
Clutch conversion i went for a seat hydro clutch/cable
New brake servo and master brake cyclinder
New inner fuel pump
New intercooler and all pipe work and joiners to suit
Bigger brakes as you got a 8v you will need 16v hubs discs pads
Just a few things of top of my head