Be very careful about choosing to turn a hobby into a career. It does not take much to turn something you love into a job that you want nothing to do with when you get home. I woodwork as a hobby and have been doing so for about a decade and a half. It didn't take too long to learn that building what someone else wants is nowhere near as fun as doing your own thing. In fact, it sucked the fun out of the hobby to a large degree. I'm much pickier about what I do now, and I enjoy my hobby more too.
When I was first going to college, my plan was to get a degree in Mechanical Engineering and go into exactly what you want to do. There was a lot of reasons why I ultimately chose a different path, but not wanting to ruin my passion for firearms was one of them.
I would keep firearms a hobby, and just go into a career that pays well enough for me to thoroughly enjoy that hobby.
If you really want to get into firearms, maybe try being a gun writer on the side. As far as the firearm industry goes, that's probably one of the easier and more flexible careers to get into. Especially since many places are online only now. Don't try to do it as a job, at least not at first. Just write a few things, see if you can get someone to buy and publish them on their site. There no risk other than a bit of your time and effort. Who knows, you might get good enough that you become one of those writers who gets to travel around the country, go to SHOT shows, and shoot cool guns for a living.