I'm going to be getting a 5-speed '91 Legacy wagon for free here soon and i am wondering what kind of performance upgrades this model will handle. All I'm used to dealing with is my '87 GL so I dont know what design differences there are. I could use as many ideas as possible.

congrats on getting a free legacy!

go here:

bbs.legacycentral.org

use the search button quite a bit before you post. nearly every question you could possibly have has been covered at least once.

as far as the most power for cheap, that seems to be a low boost turbo setup on mostly stock components.

First tip:

 

Try the new gen forum - you know - where the legacy people are