These are some early customizations that made sense and feel pretty good so far. They account for Windows and Mac usage, and have special affordances for Vim, tmux, and general shell life.
I've got DIP switch 3 turned on, so Caps is a Fn key. After many years of using Caps as Ctrl, it will take a little while to acclimate. However, the modality is generally comfortable after a surprisingly brief period. Having arrows and navigation on the right hand home position is very nice and has taken the edge off, because navigation is so common. These arrow chords are the same as I am using on the ErgoDox EZ, which helps keep things consistent.
Because there is no bezel, left Ctrl is pretty easy to palm. This is still not totally natural, particularly for my most commonly used scrolling in Vim: Ctrl-u, Ctrl-d, Ctrl-e, and Ctrl-y. I figure that these will come along or that I will grow accustomed to other navigation (e.g., {, }, zz, zb, z-enter) rather quickly since I have chosen not to make affordances for them with Fn. In part, they have served as fidget strokes because they were under my fingers, so I am not too concerned.
This is where the magic happens. So far, I only live on layer two. There is only one key that is mapped differently without using Fn: Escape, which is set to send backtick. Fn-` sends escape.
Some chording niceties for navigation and text editing:
s: Shift -- works as a regular modifier, left Shiftd: Ctrl -- right Ctrl (just in case I want to do something special)f: Win -- left Wing: Alt -- left Alt
A few shell/Vim survival items:
a: Ctrl-a -- for tmux sequences, especially Ctrl-a twice, or followed by arrowsw: Ctrl-w -- for Vim window sequencesc: Ctrl-c -- most common and quickly needed control sequence at the shell[: Esc -- convenient escape, muscle memory from years of shell/Vim
Speculative text editing accelerators:
Space: Backspace -- for a few characters/words, this is very handy;: Enter -- why move two keys away?': Hypen -- a little homage to Dvorak; dash on pinky always felt great- '': Insert -- since Insert moved, put it near delete
Things I'll probably hit by muscle memory, but don't want to assign yet:
e: Shift -- mask Next with something harmlessy: Shift -- mask Calp: Shift -- mask PrtScr
This arrangement makes for extremely comfortable text movements and navigation with modifiers. They follow the physical key order, sort of getting progressively stronger to the right.
I always swap Cmd and Opt on the Mac to get the usual arrangement in software, while leaving the keyboards with Win and Alt in their physical locations. This makes the keyboard trivially usable with any computer.