exhaust system help
 

I have a 2000 Mitsubishi eclipse GS with a brand new engine. Ever since I got a new engine all my old parts are falling apart. Etc. I fixed most of it so far, was having an overheating problem and had to replace the radiator, radiator cooling fan, got a new IAC for free, got a thermostat for free, now getting a new water pump for free on Thursday.

One of my catalytic converter went bad and now needs to be replaced, but I want to get an exhaust system. I want to know the steps of getting one and what to look at, I am interested in a invidia N1 exhaust, its a cat back so I am going to need a downpipe to? I'm open to any ideas and help please. Any websites would be appreciated to