With respect to the Impostor Syndrome, as a developer with 35 years in the industry and a non-technical degree (albeit lots of technical skill and interests), I can tell you that it never goes away. It is the sign that you are challenging yourself and learning new things. If you ever lose that feeling, move to a project or job doing something new. In technology, if you aren’t in a little bit over your head, you aren’t keeping up.
I love the Raspberry Pi suggestion. Play with that as much as possible in your spare time, in each of the above languages, and you will grow like a weed in the software industry.