“Ashes’ Will” – “A Sad Journey” [Campaign 2, Mission 2]

It's better not to take Chaos at all. Without Chaos, it's not that fun. Summoning with Darkness is more important, and three schools is clearly an overkill. Darkness, Summoning, Education, Logistics, and Sorcery are the optimal choices for the campaign.

Maybe; I'm just doing it out of a long-standing habit from Heroes 4, giving the mage Warfare and +3, or even 4 schools, turning them into an Archmage, and for everything else, there's a second hero-tactician in the squad, of the General class, who specializes in Warfare.