To answer your questions
Stage 1: Buy an MD376 TurboDymanics turbo
Stage 2: You can send your own turbo - they can hybrid your turbo in about a weeks time.
Stage 3 and 4: Who is your prefered choice of tuner? I highly recommend AmD Essex for the work. Kenny@AmD has done quite a few big turbo TDIs and got brilliant results. He got out of mine 226BHP and 380LB/FT of torque. Volvic who got his done yesterday got decent results too, 223BHP and 340lb/ft of torque but his turbo was a turbotechnics one.
I cannot speak of AmD highly enough. They know TDIs and what is needed - they are the only people who touch my car. If you ring AmD speak to ben or shaun and say I sent you. They will sort you out.
Things you will need for big turbo.
1) Sachs uprated clutch
2) Miltek DP
3) OE FMIC pipes and uprated clamps. The standard SFS stuff cannot cope with the extra boost.
4) Diff if the money allows
5) As many suspension mods to handle the power as possible.
6) 312mm conversion at least. Make sure you get good brake pads DS2500's.
If you havent already, read through my thread from Big Turbo onwards. Thread is indexed so should be easy reading. Shame your not closer, would have taken you for a spin.
Hope this helps.