Ko3 turbo

I know this doesn't answer your question but seems a great price for an upgrade in my opinion ko4 kit in classifieds

There is less to do with a K03 hybrid in that you do not need to move the diverter valve to the front of the engine and so will not need a new throttle intake pipe. A preowned K04 will be cheaper if you can get a lightly used one. I believe the BBT 360 was a well regarded K03 hybrid.
Both will need updated injectors from something like an S3 8p and an RS4 fuel valve. Also I think the map sensor needs upgrading.
You will never make tuned S3 power on a BWA as the engine is not as strong.
As mentioned above, keep you eye open for 2nd hand bargains.