With Zombies, it's better to go for the Sorceress's Castle in the first week rather than rushing to help the main hero.
In general, there are very few quiet, peaceful scenarios for calm development. These include Beltway, Good versus Evil, Teleports, Overlord, and Tundra. Some medium-difficulty scenarios are simply a quiet horror. I couldn't complete Undead Armies as a Wizard on King difficulty for a long time. I finally managed it by sheer luck, managing to defend against the Knight and capture the Sorceress's Castle on the 8th day. Otherwise, in every other scenario, the Sorceress hangs out with 100 goblins she has looted, the Knight has a decent army, but you can't build your own Castle, and the second hero is killed without an army. In general, it's even more challenging than Pyramids.