I take it you cut the old downpipe off or it had already blown apart at the flexi joint like my S3 did.
I changed the downpipe on my S3 whilst the head was off as the old downpipe to turbo bolts had rusted and rounded, it was impossible to get them undone + I had been losing coolant and assumed a head gasket failure + it was due a timing belt so all at once.
I also fitted that same ebay downpipe on my TT whilst the head was being rebuilt and forged rods fitted after a happy accident.
Doing it this way meant the support bracket needed removing but in both cases it worked out okay. but the Subframe is a relatively painless approach.
YES you need bolts they are about £36 from SEAT, SKODA, VW, AUDI dealers and a 27mm socket and a 3-4' breaker bar and a big torque wrench
but after I reversed over raised ironworks I broke my ebay downpipe up by the turbo, so bought a posh pipewerx version (just exactly the same as the ebay version apart from I bought it with a sports cat then fitted a decat pipe, to save the sports cat for sunday best (eg MOT)
if you are not in a hurry have a think about what else you might do.
1. If fitting a 3inch downpipe you need to uprate the main bush in the dogbone engine mount to a powerflex bush (yellow?, some people use the diesel red one, and I think black is just soft like your worn out stock one). if you dont do this, the engine torque will make the downpipe hit the tunnel, propshaft etc and put extra stress on the flexipipe etc too
You remove the dog bone mount first and fit it last - this is so you can sort of tip / rock the engine to help inch the downpipe up past the prop shaft and tunnel
2. the car needs to be aligned after moving the subframe
. <- I left the steering rack connected and you can fit the 3inch downpipe by carefully moving this out the way but must be cautious you dont damage, crimp etc any of the pipes etc. you also need to get it back as close as you can as the subframe is connected to the entire front end alignment components.
3. do you need new drive shafts - or cv joints or boots? - I have bought both drive shafts for my S3 (when one CV joint was clunking off when reversing and then properly worn out after showing off to my kids on the way back from Thorpe Park shark hotel stay - coming off roundabouts #fireUptheQuattro
I also changed both on my TT when one inner boot had been split for a few months and the outer boot had also split, and I was fitting the downpipe as the driveshaft outers need removing (may as well remove both)
These were £89 for the pair in both cases from J&R and have been problem free in both cars (not everyone agrees, but it is usually people who paid £400 a pair said they would never waste £90 on a pair again
) it is much cleaner and easier than taking apart drive shafts fitting boots etc. and as one was split for months that joint would surely need changing.
4. do you need track rod ends? they are £8 each and you will probably want to remove them anyway so you are not yanking the steering rack etc
5. do you need lower arm joints? the bolts need to be replaced in any case, they may need cutting off anyway and you will probably break the boot trying to remove it - and if you are replacing them you dont need to be super careful when removing them. about £30 a pair (not sure I quite remember but not bank killing)
6. are your steering rack boots okay ? that is another £12 a pair
(Some rich people totally remove the sub frame and service that, change those bushes and also replace the wishbones.)
Remember you are under a car and it weighs a lot, use the correct support stands tools etc, and if you wear glasses put an old pair on to protect your eyes from falling debris and tools.
good luck, update us with your progress.