> What's a good way to get started learning to build/customize shaders with GLSL?

I gave some directions and resources in a comment here, it might help you: https://www.reddit.com/r/GraphicsProgramming/comments/1pgqis...

> And GLSL syntax looks a bit tedious to be honest, but I'd love to dive in.

With the vectorization everywhere, it's surprisingly convenient given how simple the syntax is. I personally just miss some sinpi/cospi/etc, and/or a PI and TAU constant.