This is a layout for a 4x12 grid layout Planck board with 3 custom layers and a bare-bones adjust layer. I've kept the layers sparse and tried to keep symbols close to where they would be on a standard staggered layout when possible so I don't have to rewire my muscle memory.
I've generally tried to avoid having to hit the shift key for symbols so there's some duplication on the symbol layer. To me it's worth it since I'm using grid layout so I have the extra keys to support this. I find typing scoping delimiters like brackets and braces is much nicer only having to hit a single thumb key instead of two thumb keys or thumb + shift.