after studying the schematics, board-layouts and parts-lists of the different adafruit powerboosts it became clear that keeping the whole project hand-solderable would be tough - considering that the powerboosts are build around a boost-converter (and sometimes a lipo-charger) that only comes in a QFN-package - which seems like too much of a hassle to solder without access to a reflow setup :-(

so plan-B might be to integrate the circuit as an as-is module, with (wire-)bridges from the carrier-pcb to the powerboost-pcb?

like this maybe?