First of all, in the Warlords expansion, the developers kindly provided us with the ability to find out what danger a particular neutral creature poses to us. "Medium danger" means the strength of the neutral/enemy army is comparable to yours. "Low" means 1/2 the strength of your army, "very low" means less than 1/2 the strength of your army, "high" means the army is stronger than yours, and "no chance" - well, that's obvious)). Secondly, the start depends on the hero you choose. It's easier to start the game with heroes who specialize in ranged creatures. Also, some heroes have an advantage because they start with a spell.

I don't really pay attention to this. I've beaten enemies with "no chance" twice. Apparently, this system doesn't take into account the players' abilities)).

Regarding the topic:
I mostly play as the Warlock, and now I'm playing a lot as Lethos. I do this: I build a tavern (if it hasn't been built yet) and then upgrade the War School, buy a second hero, upgrade the Scouts to Rangers, and go to clear out everyone with plague, without any losses, I can even take out quite powerful (up to level 4) neutral creatures. I quickly gain levels, and so on, until the beginning of the third week. On that week, I return to the Castle, buy all the troops, and go to the enemy. I also level up Chaos and either Sorcery or Education, as a result, I have enough mana for both Chaos and Darkness.