The most challenging maps for you.

In my opinion, he should definitely have Earth and Water, highly desirable Air, and if possible, Fire.

What is this perversion? :)))
He should definitely have: Leadership (starting skill), Water and Wisdom (walking on water), Scouting (to reach the island with Cyclops, although you can use 2 heroes with walking on water), Logistics (obviously), and then it's up to you. You can choose Pathfinding, or Armor/Offense. But taking 4 magic skills is definitely not a good idea. 2 elements are more than enough.