Has anyone got any good resources for something like this? I haven't touched C in years, and never worked on anything game-like. But it does look like a really interesting project to start something like this.

If you have patience, the first 30 or so episodes of Handmade Hero are pretty good.

https://guide.handmadehero.org/code/

raylib is one possible starting place. Also might look at dos-like (https://mattiasgustavsson.itch.io/dos-like).