Originally Posted by ripemeat
Your LGT certainly isn't challenging like some people on this forum make it sound. Literally just bolt the parts on with new gaskets and get a tune or accessport- plug it in and load the map and you're done. a downpipe and an accessport w/ the provided stg 2 93 map could get you a gain of 50whp, all for under $1k and maybe a couple hrs in the garage.
^ This. But as long as you're doing the downpipe, replace the uppipe too. If your car is still stock, the 05's have a cat in the uppipe. By removing it your turbo will spool a little quicker and you have eliminated a cat which has been known to come apart and take out the turbo or engine in the process. That is why this cat was eliminated in later models. You should be able to pick up a used STI uppipe for $80 shipped here or on Nabisco.
Furthermore since you are fortunate enough to have gotten a new engine, I would recommend putting a few thousand miles on it to make sure there are no issues with they would then be denied under warranty if you had any mods.
Also since you have a 5eat you can increase the line pressure in the valve body by using manual mode or sport mode. This will help save the clutches if your asshatting around.
Check and change your oil often on these cars. That is one of the biggest causes of engine problems with these cars.