Demon invasion.

Pao Archipelago. I captured all the castles. I watched three videos. Nothing happens next. I can't move around. What should I do?

I understand that my comments and playing this campaign are a bit outdated, but still :D
The first campaign about the League of Shadows was playable, difficult, long, with replays and restarts, but it was passable; I played it to death and spent a total of 100+ hours on it. Here, I restarted the first part of the map for a very long time until I finally got a leader and spent 40k on the mentor (I didn't even count how many attempts it took). I understand that the author tried his best to minimize the importance of randomness, the must-have artifact is a wonder, but without a defense roll at the first levels, most stacks won't be broken, and if the starting stacks can't be broken, it's just a restart. Then, I honestly don't understand what kind of wizards are sitting here on the forum, but I only managed to defeat the angels and the library when I managed to find the Tome of Power along with the Artifact and the leader of that faction, and even then, one stack of imps remained in a slot. I defeated the rest of the demons only by the fourth month because I had to run around all the castles where two of them were stationed. But then an even bigger problem arose because I emerged on the surface, my stats were at zero, the hero was practically naked, and there were stacks of hundreds around me. Cerberuses, furies, harpies, and other pleasant creatures; how to defeat them with a spell power of 1 and without BPD, not to mention without losses, or even just to win, I honestly don't understand. Reinforcements from the Castle don't seem to help either; the stacks are huge and extremely unpleasant; I don't know how to kite and defeat them. If I try to get out of the valley into the snow, there are hundreds of wolves. And all this with a warrior. I watched a walkthrough of the map, but there the spells dealt 4 times more damage and cost 5 times less, so it's some kind of nonsense.
In general, dear wizards, I have read almost all the discussions and seen the builds, but I'm just stuck at the very beginning, so I earnestly ask, maybe someone can just write down at least an approximate plan for completing the game and in what direction and within what time frame I should move and where? I would be very grateful.