1. The bottom left key (Cntrl) is L1. I chose it because it's easy to just lean on it by the side of my palm as opposed to pressing it which is a hard to reach point. It controls commonly used hotkeys like window management, media (vol, play/pause), clipboard etc.
2. A layer for symbols & fn keys.
3. A layer just for VS Code keys. For instance, Ctrl + Page Up/Down behaves like mouse scroll (on Mac), so I've dedicated layer keys around home row. It's naturally placed near home row navigation. I also have some handy macros like that will type language specific stuff like "() => {}" and move cursor inside parenthesis, etc.
4. Another layer for pretty much everything else. Like, locking & unlocking my Mac (bad practice to have pwd in macros, I know), opening "about:logins" in FF, tagging files (Ctrl 1,2,3...) etc.
Pro Tip for newbies: 1. Get comfortable flashing new configs (which shouldn't be a problem these days)
2. Don't over optimize layers & macros - go with something decent that will solve major pain points.
3. While using, make a note of things that work, things that feel odd and things you never use. Then, make incremental modifications. Rinse & repeat.
For people considering Mech boards: It need not cost an arm & a leg. The first board I bought was Tada 68 which cost around 120 bucks. Getting a board with swappable keys might be tricky at this price point - but if you know what sort of key you want, this shouldn't be a big problem.
As with SW development, start simple & expand based on necessity.