a 1.8L WHAT??
I will assume you are talking about a impreza, and based on that here goes.
I would pick the Legacy Turbo turbocharger if one is avalible to you. If not the one off the older subaru Turbos will work. You then have two choices for exaust routing. You can get a legacy turbo crossmember and exaust, or run a minam style setup. Intake plumbing is dead simple once you have the rest of it done.