1N14 is a model of Nixie Tube use in some Nixie Clock projects.
That's as good an answer as any..
in practice NTP doesn't care much what is in those 4 bytes AFAIK. You could try with different values and see what happens ...
(don't poll NTPservers more than once a minute, they don't like to be flooded.)
No, they're entirely arbitrary - except for the case of stratum 0, where some combinations of characters are used to rate limit clients... precisely related to your last line.
Personally, my NTP server broadcasts to the network once a minute, so as it stands, the arduino never has to request the time anyway.
Thanks for the replies guys.