Stage 1: 2 layers:
- stage 1 design
- set modifiers to thumb cluster
- combine FN-# layer and mouse layer
- FN caps-lock for now?
Stage 2:
- sticky modifiers: press both modifiers (left and right) to get sticky modifiers, press again to release, e.g. Left-Shift + Right-Shift = CAPS Lock
- tap-and-hold for temp layers?