Disabling caches in Safari results in server errors while developing Craft 3 site
If I change the mode to "production" from "dev," the errors go away,
  and as far as I can see no new error is created in the server or Craft
  log. So I can develop in production mode but I do find the dev mode
  useful.


It sounds like you're changing the environment variable ENVIRONMENT, e.g.:

ENVIRONMENT="dev"


This actually doesn't do much, it's just an arbitrary name for the environment that Craft is running in. You could call it fluffybunny and no one would mind. The only thing it affects is what settings might be used in you multi-environment config files like config/general.php.

I'd suggest reading over the Flat Multi-Environment Config for Craft CMS 3 article

Also for log file reading, the article Zen and the Art of Craft CMS Log File Reading may be useful as well.