Sounds like a pretty fun project. The 3SGE is a very stout motor and will take to turbocharging really well.
I would look at the BGB's for both engines and figure out which parts to swap over to make the car run on the ST205 ECU, or perhaps scothaniel can provide you with a more detailed list. This would be an excellent route though, this way you have a solid and accurate fuel tune, plug and play.
OEM Parts to consider from the ST205 are:
-ST205 ECU
-Complete harness, or overlay the wiring diagrams and just add on the wiring that isn't present on the 3SGE harness thats needed to run the 3SGTE ECU.
-Any additional sensors (Turbocharging VSV, MAP sensor, etc.)
-3rd gen 3SGTE CT20B turbo and manifold
-ST205 Fuel Pump, or TT Supra/Walbro 255LPH.
- ST205 side-feed fuel rail and red-top injectors
- Throttle body? Distributor? etc.
I would definately talk with scothaniel from these boards about his setup, he could probably steer you in the right direction more so than the rest of us, but thats a general idea of what you'll need to get started.
Good luck.