b4subaru

Just wondering what would be the best way to start should I do a turbo back a cat back exhaust before I get the car tuned and focus on the rest of the car which is the best way to start ..

Not sure where to start as I am only new to the scene.i just got a 2002 b4 liberty which I have wanted for a long.the problem is my lack of engine knowlege but I am a quick learner so would really appreciate any help so I can work on the car my self and save money ..the car is running rough the problem is when its sitting on about 3000rpm it seems to surge up and down and feels like its about to stall when coming to a stop or idle.it dsnt seem to have much boost at all and as its hard for me because I have not driven turbo cars before.however I have been in plenty of them and from my experince I can feel its not running as it should.any help or suggestions to help me get this car into the 200kw atw it should be would be much appreciated ..