The things I wish I learned better in school are things like trig, which would be nice because I’ve developed a little interest in things like machining

I see that you’ve watched some videos, and you should definitely continue that. I teach HS physics, but I never took an actual trig class because of an administrative quirk. I thought I had this huge gap in trig but eventually I realized that there’s just not that much. You can definitely teach yourself trig!

Khan Academy is great, but the secret sauce is in really trying to understand WHY you get some of these problems wrong. If you really spend some time trying to find each mistake, and thinking about what exactly makes it a mistake, you’ll be all set.