What should I check when buying a used Mazda 3?

So I’ve been looking for a car for my daily commute into Portland since my old Civic finally died on me last week. I’ve got about 12k saved up and I really want a Mazda 3 hatch because they look way better than anything else in that price range. I’m hoping to find something within the next two weeks because carpooling with my roommate is getting old fast.

I did some digging online and saw people talking a lot about rust issues especially on the older ones but I’m looking at the 2014 to 2017 generation and I’m not sure if that’s still a huge deal or not... also I read a bunch of threads about the soul red paint being super thin and chipping like crazy. Is that just people being picky or is it actually something I should worry about for the long term? I’m also kinda confused about the different engines like is the 2.5 worth the extra gas or should I just stick to the 2.0 for better mileage. What are the specific mechanical red flags I should look for when I go to see one in person?