Pillars of Eternity: Complete Edition

If you don't want to wait and gather an army. Set the game to the easiest level. I took the fortress with lvl 8 characters. Only paid 10,000 for veterans. When they wrote that I was supposedly screwed and had a choice of which squad to kill, I chose to go on the attack myself. After the text quest you will be thrown onto the battlefield. Everything will end there.

You can take your time with the quest, since it’s still better to accumulate allies and your own strength. In terms of your own forces, everything is clear - buying barracks and hiring mercenaries + rare “story” and not so mercenaries.
Allies are any forces that, during the course of the main plot and the plot of the 2 parts of the DLS, will fight with you (Knights of the Horn, Dozens, Domnels), Ogres and Flails from the White Passage.
Not sure about the White Walker Paladins.