Update: making custom cables sucks!
The crimp contacts and housings appear like they would mate, but every time I crimp a wire on and try it insert it, more often than not the wire snaps off. The specs for the contacts say they work with 20-26AWG, but my 22AWG hookup wire doesn't seem to fit. Thin solid wire taken from ethernet cables (I think 24-26AWG) bends very easily and snaps.
This process appears really straightforward, but is turning out to be the most frustrating part of assembling my project! Am I doing something wrong, or is custom cable assembly best left to machines and factories?