(1) I went with the Summoners, the same as for the Knight difficulty, because they are well-situated to spread throughout the southern half of the map. (2) This route relies on getting allies in one of the two ruins in the central island; here I got two Ghosts. (3) I had good luck in getting to the cities on the Eastern island before anybody else; this usually doesn't happen. As it is, it appears I arrived just in the nick of time!

It's hard for me to see a lot of improvement with this route, except perhaps for quicker decision-making after getting the ghosts. However, I can imagine a faster route existing for the Druids (green) or Magicians (white), if they get strong allies on the first turn.