My questions, then:
1) What would be a casual greeting between two university-aged boys? I've made use of a Welsh-English online dictionary and a couple of websites listing common phrases, but that doesn't tell me much of what greeting would be used in what social situations. I've got Prynhawn da currently, but that sounds awfully formal to me.
2) I have one character saying "Iesu mawr" in mild exasperation -- one of the boys at university. Is that something he'd actually say, or should it be Iesu Grist or what?
3) In 1980, when a train pulled out of the station, would those on the train hear a whistle, or an announcement of the next station, or would the conductor come around collecting tickets, or what?