This can be quite a task.

1st you need to open package managers add EBM mod as a depending mod. Its not a mod I'm to familiar with.

However after that I think the main rpk you need to open is Aow Unit leader.rpk, Unit leader DLC2.rpk and Unit Leader DLC3.rpk where heroes are.

Then the corresponding Aow_Lords.rpk and the dlc ones to add leaders.

If you just want to add hero I suggest to copy hero that is edited and see what's been added. You cannot directly see what's been edited without double screens. But copying something will add whatever changes DerMentat made to heroes and you will be able to work from those entries to add whatever EBM mod added to heroes in order to make new ones based on that

If you are unsure what you are doing it might be difficult to invest time in it. Creating heroes mod is not exactly brain surgery, but it might be more difficult to add things added by someone else.

The main issue with creating heroes is that you don't see result.

However, there is a way to see.

Play game in debug mode. It's a cross box in the Aow III launcher and then launch the game.

The create a leader in game in the menu as normally. Press Ctrl + alt + D and all editor names should show up as they are written in the mod editor like "Human_FullHelmet01" etc

Then just take a print screen and add the same values in mod editor.

Yeah the thing is that it's easier to just copy a hero that's already made. Edit the copied one, tweak values to liking and add your own custom first and last name.

Adding skills and abilities it depends. Most heroes has everything a leader has but 1-2 extra fluff abilities that might not be available otherwise.

Some heroes has life steal, others inflict stun etc.

You can check what vanilla heroes has to see what I mean.

https://age-of-wonders-3.fandom.com/wiki/Heroes

Dunno. Since you use EBM as a base its difficult to say what the issue is and how it's set up. There could be something that heroes get something more defined in class skill upgrade as it could be researched through avatar skills and added as permanent addition as EBM specific edit not seen in hero section.

Normally, it would not yield this.

At base, a unmodded hero always has 10 extra skill point for each spell. A warlord could have lv1 "last stand" costing 5 skill points and lv1 "Shout of imitation" costing 5 skill points.

Making it start with two spells and no skill points since its depleted.

Some vanilla heroes could be seen with 13 points. An Arch Druid could have 2 spells 5+5 making it 10. Then 3 points gone to "Befriend Animal" since it could be his special and then applied as a total of 13 points in total depleting it's skill points since it could be picked on level up for arch druids.

Adding something like absorb pain on a Dreadnought taken from a theocrat could potentially not deplete skill points since its not part of that class hero skill tree anyway.

Setting more than 10 extra skill points makes hero so incredibly strong it's almost ridiculous how op it will be. (Normally, heroes can almost solo entire battles themselves) ^ ^

Great good luck and have fun,