uhh if you are ever going to install the bushings you should do it before you put the arms on otherwise you are doing all of the same work twice and running a risk of messing up the ball joints when you remove them. once you buy the bushings its an easy install.
i also believe that if you buy...
Diamond motorsports has urethane bushings you can press in. I did it to my car it wasn't that bad once I warmed the bushings up and made a huge difference. Depending on your mileage might want to start with brand new control arms from the dealer
do you have your stock map sensor to put back in? at spring pressure you are still in its range so you can determine if the CS one is going bad. does require a change to the tune though.
do exactly what @Crazycanadian said about bypassing the ECBS entirely to determine if you have an issue with...
@phate I feel like you might have been down this road
These cars are a bitch to bleed. Make sure that you are bleeding the clutch at the same time. Many people have found they can only get an acceptable bleed with a power bleeder
ok that is a different scenario than what your post seemed like
would you make more power with an upgraded exhaust? yes. is the stock exhaust going to stop you from easily hitting your goal? no.