Are changing pipes necessary? Or if anything, cutting, welding and reducers the cheaper way to go?
And is it bad to buy them online even if they're cheaper? Or should I go to a local performance shop?

 

it all depends on what you want to do... if you're doing an entire exhaust system, then i would just buy everything from summitracing.com or wherever. there's nothing wrong at all in buying parts online. however, if you're just looking for a catback, then it's easy enough to get straight pipe, make a few bends/cuts, and you're done. i would just go with the complete kits. that way, you know everything will fit properly and you wont have any unnecessary issues.

 

Exactly, I was looking at a few kits online and I thought well this would save a lot of time and work. Any kits that come with high flow cats?