When implementing my own scripts, is it the best practice to exit with different exit codes for different failure scenarios? Or should I just return exit code 1 for failure and 0 for success providing the reason on stderr?
Providing a descriptive error message to stderr is fine and well for interactive users, but if you expect your scripts to be used by other scripts/programs, you should have distinctive error codes for different failures, so the calling script could make an informed decision on how to handle the failure.
If the calling program does not wish to handle different failures differently it could always check the return code against > 0 - but don't assume this is the case.