<BTW, my brand-new exhaust system
already looks like it's 4-5 years old, complete with a rusty tailpipe.
What's up with that?>

Pretty typical. I think the tailpipes start to rust in shipping. Unless you spring for stainless steel or take the parts somewhere and have them professionally coated, they rust in short order. You can always paint the parts with Rustoluem BBQ paint-that lasts about 2 weeks.     Jeff