Regarding the skeletons:
I decided to try it out. I took Vedomina, leveled her up to the third level, and made her an expert in Necromancy, catching up with everyone as expected. I just didn't build the enhancer right away; I was a little late with it. There was no talk of 3,000 skeletons; there were only 500-600, and the meeting of the main heroes was already approaching. I guess if you play for three months and don't attack each other, but just accumulate skeletons, you could gather that many. But I prefer to play aggressively, so I choose an early attack, if possible, and even on HL maps, I rarely play peacefully for more than three months. :)
Now we're playing against the AI. I only have 250 skeletons, and they all died while I was taking castles from the AI and defending my own. My starting hero is Vedomina. After leveling up Necromancy, I upgraded Earth to Expert and, after building the Guild to level 3, I failed :((( But I have Tant now, and now I'm looking for a hero with Lore, so I can teach Vedomina the Resurrection spell. For now, I'm betting on Berserk and Expert Fire. Against the AI, it's a super spell, especially when defending a Castle. Even without Fire magic, it helps a lot in winning battles.