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Cool mission :)
I started by playing with someone else's save (until I killed Koly from the previous campaign :), but I still tried to capture the city as quickly as possible. Then I abandoned that save, finished playing as the Elves, and started a new game as the Mage. Since I already knew where the city was, I calmly went around the map through the northeast-southwest, captured it, and then started capturing mines and various places that increase knowledge and defense/attack, trying not to gain experience unnecessarily. At the same time, I built a 5th-level Mage Guild in the city (there was a problem with gems, so I had to spend time trading and just letting days pass). In general, when I built it and learned everything I was capable of (I learned only one spell at level 5, summoning a Phoenix), I went and killed someone else, and the mission ended :)
At this stage, I took only Light and Sorcery as new skills.
I also want Luck, something from Attack/Defense, and maybe Chaos.