pinion depth, how close does it have to be

The number on the pinion is nothing but a guide to get you close. Sometimes you're dead on using that number. Most times, you're just close. Sounds like you got it zoomed right in.
I'm not proud but it took another solid 5 hours to get it all done today including the spacer preload.
Zero lash that's wild! I'd be interested to hear the break in procedure if it's any different