You can make it work by piecing it together, but as mentioned - Its rediculously fiddly, painfully hard to get the right parts (even the top radiator hose connection on the motor is different between 99 and 02 TT motors, despite being the same motor). Looms are different between models, and same with ECU's. Add that to the fun of different sensors on various motors, and the ECU and loom you get may not even get the motor to fire up.
It will be about twice the price too, as you will have to pay for every single part rather than get a complete package.
Sorry for the bad news, but I believe you have rocks in your head if you want to piece it together.
As for the heads question - You can use 2.5 heads, but not the ones you have without major modification. The flows arent there, and the cams are pure and simple not set up to run forced induction. If you wanted to run 2.5 heads, you would have to source some ADM 2.5T heads - the japs never went away from 2L turbos in the mainstream. On top of this, the N/A injectors will not flow enough fuel to make a turbo build any good.
Your second question - No. I could go further here, but the simple answer is no. Its the same as the engines - it depends what model it came from etc. Lots of differences between them. Compression ratios vary, stroke and bore is different, piston top design and overall strength varies by a lot etc.
Hope you dont take this the wrong way man, the amount of headf#&ks this will give you is incredible. There are reasons everyone starts with a base setup rather than starting from scratch.
MY00 Red RX, a nice daily that was sold off once the B4 became reliable...
MY02 Blue B4, aka 'The Project' - v8 JDM STi engine package and assorted other 'goodies' - Sold, then bought back for parts. Stripped and crushed.
MY03 Blue RX, the newer old daily, pretty well more B4 than RX now... In the process of being converted to the track toy... Watch this space!
MY02 Silver Wagon, H6 conversion, full blue/black leather and almost full black interior to go with it.
MY03 White/Silver H6 Outback, donor car for silver waghoon.
MY97 Silver RX, acquired to become track car, but plans changed. To be stripped and scrapped in time.
I can pick up a ej20t for $200 pretty much just engine will need manifold an turbos etc
