http://alexmars.com/FW_editor_guide1.htm
Here is a guide that I used.
There are some old forum posts about map making also.
There wasn't any Fantasy Wars map editor official documentation. The map editor is in English. A little bit of it is badly translated. The game itself doesn't have that problem. I have no idea how Elven Legacy editor will be as far as the translation and documentation goes. I assume it will still be easy to use.
Setting up the AI is just setting modes. It isn't like scripting actual AI. The AI makes most of the tactical decisions on its own. Like attacking heroes first. If you don't tell units to defend areas it tends to group together in the best terrain possible and attack once you get in range. You can change the modes after something happens. Like moving troops to the first city attacked. The troops might attack something in the middle or not go if there is a lot of water in the way. Most of the campaign just has have some enemies defending cites or special sites and some troops that move to reinforce things. The AI doesn't seem to know about your position until it sees you.
I don't know what Elven Legacy has changed.
The only triggers you'd need for a chess type pitched battle would be for victory situations and when the different sides could place units. All of that could be copied from existing maps. You wouldn't need to set anything in the AI. If you wanted to units to move from somewhere else on the map, appear on the map, or defend something you'd have to make triggers for that.