I have a hole in my exhaust in the flex pipe and am wondering if I need to replace just the flex pipe or the whole down pipe or if the flex pipe even needs to be there? Would it hurt anything to replace it with normal tubing?

Also I have been looking at getting a new cat-back. I know the exhausts on these cars are very restrictive and there is a lot of power to be made. I'm guessing most bolt on exhausts are $500+ so I will probably get a muffler and have an exhaust shop weld one up. What is the best diameter for a stock AWM 1.8T and will I need to get a boost gauge and or worry about boost creep?

 

You do need the flex section. One can be welded in to replace yours. ECS sells them. On a stock tune you won't gain all that much power from a catback (the gains grow as boost is raised), but you're looking at $700-1000 for one. Buy a muffler and have the rest made in 2.5" and you'll be set.