aftermarket system

Hi all, looking at picking up a 2018 lacrosse fwd with the 3.6L v6 with around 50k miles, but was wondering if there were any recommendations for exhaust systems, most likely mufflers or a cat back system. I am aware this shares similarities to some Cadillac models like the ats and cts, and...

I have a 2018 Buick Regal sport back. It’s the preferred trim model. It doesn’t have the Bose system. I already know the factory stereo can’t be replaced. Can anyone provide and instruction and how to install the amp, speakers and subs? As well as where the wires would run?