Uninvited guests.

My mod conflicted with some other map (I still don't know which one) – the Twilight Dragons have 3k HP and cast Fireballs at maximum power... It's quite overpowered. That's why I immediately retrain them into alternative subtypes. Otherwise, the game quickly becomes uninteresting.

You just need to clean the "maps" folder from other maps.

I wanted to take Iran with her agile Furies as my second hero. But she wouldn't appear, no matter how many times I reloaded the map... It kept giving me Orcs, Demons, and Humans... I only saw Vaishana and Letos from the Dark Elves. I stopped at the latter.

You should choose the starting Castle of the race you plan to play as; then, your first hero will always be of that race, and with the second, if you're lucky ;)

"Stupid human specifications" - is this about morale/luck?

No, "stupid specifications" refers to "Super Control" and "Counter Strike," which are effective if you have a lot of units that can be hit many times (I try to play with minimal losses, meaning I try to ensure that the enemy can attack as rarely as possible).
And the most useless skill is "Experienced Leader," IMHO – it's a very questionable advantage that can bring meager benefits in the very distant future when you have a lot of resources and money (I try not to stretch the game out that much), while your main hero must be in the city by the end of the week, which is not always (or rather, rarely) the case. And on this small map with one city and very limited resources, it's generally not very effective.

For Humans, Light Magic is the best! Righteous Strike, Divine Might, Haste with Stone Skin in large numbers – a deadly combination, I tell you! And a fully developed Counter Strike on top of that! The enemy will be bleeding!

I'd like to see how this "best" helps in a battle against several hundred creatures of level 5-6 when you only have a few dozen, or sometimes even fewer, units at your disposal. ;)