I am doing this same swap into my 95 Legacy Sedan.
You'll need to change to the Turbo ECU (The N/A one won't be able to moniter boost).
Parts you need (as I understand it):
mounts (since your stock mounts are 8 years old, get some new, stiffer mounts).
It should be an almost dead on swap from what I have gathered. Just unplug everything from the old engine, then plug everything into the new engine.
The hardest part will be finding a low-mile donor engine. You might be able to go to your Subaru Dealer and see if they can order you a rebuilt EJ22T or an EJ22T Crate engine. Subaru has to offer something to those who drive the Turbo Legacy's and blow the engines. There has to be a good condition, low mileage engine SOMEWHERE!
I need to go to my mechanic and see what he can get for me. I'll be visiting my local Scoob dealer very soon trying to figure out the best source for an engine.
Depending on how much a donor would cost, it might avtually be worth it to buy a new engine just to know it's got 0 miles on it.
I have a question though:
When you do the engine swap, do you reset your odometer to the miles on the engine, or leave it to the miles on the car?