Is there a universal way to choose a magic school in the late game (so that there are no minimum summons that fail, etc.)? I used to play as Warlocks (and realized that in the late game they are simply useless against all races, as they only have Chaos or Chaos + summons – against Orcs and Mages), but now everything seems more interesting. Please advise...

Added after 15 minutes
and one more question: at what point (1, 2, 3, or 4 weeks) should I make my first artifact (Initiative or Defense + Health) to break through quickly?