First of all, welcome to IGOTASTI!!! You're going to absolutely love it here!! Post some pictures of your Blobeye!
Your wording is somewhat confusing. Right now, you have a "stock motor and tranny." Does this mean Impreza, WRX, or STi? "WRX rear dif and axles." I don't know exactly what you have, whether they're all from one set or if they're a combination of Impreza, WRX, and STi parts.
Here is what I know: If you want to swap in a motor from an STi, then you need the following at the minimum:
-STi complete motor assembly with TMIC and turbo
-STi ECU
Then, you have the choice of going with:
-STi complete transmission
-STi driveshaft
-STi rear differential
-STi axles, all 4 corners
-STi knuckles, hubs, Brembo's
-or-
-WRX complete transmission
-WRX driveshaft
-WRX rear differential
-WRX axles, all 4 corners
-WRX knuckles, hubs, brakes (standard or Hawkeye 4 pot)
You may have read and heard of the hybrid setups. I've seen them go both ways, too. WRX engine with STi drivetrain, or STi engine with WRX drivetrain.
Then another complication arises. It depends with what year drivetrain you choose to go with. I think almost all GD STi models vary in some aspect, with 2004 being the biggest outlier. WRX drivetrains differ as well between the 2002-2007 models.
There's a lot of research you need to do regarding the internals of the transmissions and differentials.
I left out the suspension because they can be either mixed and matched from various stock vehicles, or you can just go all out aftermarket with the endless selections.
So, what model year STi motor are you contemplating? What year WRX or STi drivetrain are you contemplating?
Also, if you're going to keep the hood scoopless look, I'm assuming you've planned out a FMIC as well?