To be honest I find Ops post extremely hard to follow. What exactly was the delay in getting the eTA? Most are approved quickly, the only ones I know that took more than a few minutes were for people with permission to study/work and therefore a more complex situation. I even met people who applied on phone at the airport and had no issues.

What airline? Most airlines that fly in (certainly AC and LH) have very signs about the eTA.

Unfortunately it's always worth checking entry requirements. Mongolia for example last year for the first time in many many years required a $$$ visa for many countries due to some EU thing going on. Half the places I went to didn't believe me but it was definitely required on entry.

Your governments website should be able to provide up to date details.

Not just visa but other things too, did you know you can't enter NZ (or a plane there) without a return ticket?