I was considering something like this myself for my GT 2.0 TDI (currently with the 288mm set up).
I was put off by a mechanic friend of mine that said once you disconnect the hydraulic pipes on a modern VW (or most cars for that point), it becomes very hard without specialist equipment to fully bleed them again and retain the pedal firmness. Something about having to cycle the ABS pump through VCDS or VAS ? True or total tosh ?
Is it really straight forward. I guess I would also need new caliper carriers to offset the caliper ? Are you selling these as well or just the Calipers ?