2. May you be a half hour in Heaven before the Devil knows you're dead.

4. In addition to other occasions where the singing of a national anthem is appropriate, it also used to be sung at the end of gatherings (Comhaltas meetings, among other things, and certain trad music events, occasionally sessions, though not so much these days). Everyone would stand up together and sing or play their instrument - it was/is a sort of finale to the evening.

6. I have always heard both these nicknames used, rather interchangeably; but it's "land of saints and scholars" not scientists.