For those interested, I was just getting ready to head to Home Depot for a ruler and feeler gauge and saw this on StewMac -- looks pricey but super nice:
String Action Gauge - StewMac
FWIW, I've adjusted my truss rods a few times and never had issues. My Bongo was the easiest with the truss spoke wheel.
What I *haven't* done is adjust action and intonation and pickup height so this is a new/exciting project for me

The Sadowsky vid was great and I found another more specific vid on checking string height that was great too.
For those that have done a lot of work on their Maru or any other bass with a zero fret: do you find you still need to fret/capo the first fret? Or does the zero fret essentially remove the nut out of the equation when checking string height around the 6th fret? I'm going to fret it anyway, just curious of others' opinions/experiences.
Also -- I now appreciate how Maruszczyk made a truss rod route at the heel of the neck with foam in the bottom. Still would prefer a spoke wheel but you can't win 'em all I guess.
Ok off to home depot...