ESC calibration - how do I know it's good?

Using a Cube Orange with a Herelink controller. I followed the “semi-automatic” ESC calibration procedure. It seemed to beep like it should to indicate success. Is there another way I can check in the logs, or with the throttle, to verify it is a successful calibration?

All motors should start up at the same time and run at approximately the same RPM when arming. If one of them lags behind the rest it might have missed being calibrated.
Otherwise, if your copter is well balanced, you can look in a log and see if all motor outputs (PWM) are about the same during hovering.

What’s tripping me up is that with the throttle fully lowered, the motors still spin. Is this OK because of the control loops in actual flight, or do I need to re-calibrate?

That’s from a parameter setting, MOT_SPIN_ARM. Default is 10%. Most people want them to spin on Arm but you can set it to 0 if you like. MOT_SPIN_MIN is a more important parameter to set. See the Wiki if you haven’t already.

That’s what get set in motor configuration? What about MOT_PWM_MIN/MAX? Are those supposed to be set at some point?

The Wiki as I suggested?
https://ardupilot.org/copter/docs/set-motor-range.html

Yes, I did see that and that’s what I did. Thanks!