For you guys asking about hardware, I have an interactive parts list generator here. Not 100% vetted across various model years, but you should be able to search by PN for your particular application to at least find the diagram and confirm fitment:
https://docs.google.com/spreadsheets/d/1JZzBmXWmrl-4BqCT4US33ct3Nc9DUjPyhsRitjYMRFY/edit?usp=sharing
For a subframe swap you'll want the following stuff (obviously only get the motor mount bolts for your specific application):
I did an 8Y S3 subframe swap onto my 19 GTI over winter. I used an 034 subframe alignment collar kit... only because I didn't want to buy the stupid little aluminum one time use anti-slip bits.
When I had the two subframes side by side, I could not find any measurable differences between it and the old one.