Left unanswered:
2. I noticed that Tourists are listed as NPCs, but not Explorers. Unless this is implied, Explorers should probably be listed as well to save future Simmers from confusion in this regard, because they seem to be two different types of NPCs though I'm not quite sure what the difference between the two is exactly.
3. Can heirs marry townies from travelling destinations, given that they are not NPCs?