Your list is way off
You don't need an S3 fuel rail at all.
You can't use S3 injectors as they're a different fitment on the AGU sadly. You'll need something like Genesis 380's from USRT (google it)
You don't need a 4 bar FPR, it can be mapped perfectly on a stock 3 bar, and will put less loading on your fuel pump.
If you're done high mileage your pump will struggle, so you'll need an S3 fuel pump. Easiest solution is an LCR pump as it'll drop straight into your tank.
S3 boost hoses will be of no use to you at all. if you're on a stock SMIC that'll need replacing with an FMIC, and you can't fit the S3 twin cooler setup, as the inlet manifold is facing the wrong way on the AGU setup, so you'll need to get an FMIC sorted, or if you've already got one, mount the ko4, then work out what you'll need to plumb it into your existing FMIC pipes.
You also need a 3'' maf housing, although the S3 one will mount the sensor at 90 degrees to the airflow using the AGU sensor, so what you need is a mk3 golf VR6 MAF housing
Then a decent custom map
Also, probably worth noting that an S3 downpipe splits into 2 parts for the twin Cats on an S3, so even if you get the S3 twin cats, you'll need a way of mounting the 'Slip joint' A3 cat back to the flanged S3 cats. Easiest solution here is an LCR 3'' downpipe / decat, although I think that's still flanged and would need modifying.
Good luck!
