I’m really struggling with how to lay out my additional layers.
Where should I put brackets of all kinds, parentheses, underscore, dash, hash, back tick? Should I have a numpad? I just can’t decide and wonder if there’s already a moderately consensus best practice?
As others have mentioned, it’s very much personal preference. I program with 34 keys every day with three primary layers: colemak dh, numpad, and nav. After having used Miryoku for almost two years, I’ve been using Callum-style mods for the past several months, and I really, really like it.
I’d recommend taking a look at keymaps in the QMK repo – especially for layouts similar to the board you’re using. You could also search github for zmk-config repos. It’s a different firmware, but layout is layout.