My hero had the "Logistics" skill maxed out, as well as the "Tent" spell, a rapid-fire ballista, and fire arrows.
Gilraen retreated without a fight. I only managed to defeat 5 Elves with Succubi.
In battles against neutral creatures for mines, I only used Cave Demons and Succubi, sometimes using only Demons. I cast Regeneration on the Demons and used the Tent spell. Against the Monks at the second gold mine, I had to send in Imps as cannon fodder.
By the end of the week, I had cleared the entire southern part of the map, except for the Elven town – I didn't touch it so that the Druids wouldn't start causing trouble.
I was lucky with the Inferno outpost – it had Succubi and Devils! These troops became my main offensive force.
In general, everything was easy from that point on: the ballista and Devils, combined with Demonesses, defeated everyone without any losses. I only used all my troops at once against Gilraen.
The first northern town on the right fell, then the Druids :), then the second northern town...
The "Logistics" skill, as well as the presence of Succubi and Devils in the Inferno outpost, turned out to be decisive.