List of all currently available Elemental: Legendary Heroes Mods in the LH Mods Forum
http://forums.elementalgame.com/446461

Recommended XtraDeconstruct: Legacy of Magic The best mod for FE LH (mixed with CoS mod ofc)

They's all 404 not found he download links are broken.

NexusMods still has a lot of them.

https://www.nexusmods.com/fallenenchantress/mods/?BH=1

Honestly, I have found FELH mods too superfluous and promiscuous in regards of added content.

IME/IMO game + XtraDeconstruct + ChildrenOfStorm is better than the original by far if you know what you are doing. If you just want to play without much hassle (adjusting the mod to what you like, detailed careful rading of the Xtra user guide etc) then I agree: Xtra mod is too munchkin and has serious documentation/understanding issues.

Well, I wouldn't say I had some 'understanding issues' with Xtra Deconstruct and CoS :) I just don't like slovenly user-made content that doesn't fit much to original game. It's just breaking the atmosphere, adding tons of items, factions, skills, spells and so on. FELH is a game of lore and art, mostly. And it tries to keep the delicate balance between quantity and quality. Fan-made stuff knows nothing about quality, alas - only about quantity.

And another important question (that I ask everytime when a big 4X strategy game is being modded): how does AI handle with this heap of new stuff? I suppose, the answer should be 'rather badly' ;)

You can selectively disable most things in Xtra mod. (I also disliked a lot of the stuff in the mod and removed it.)

About the AI: Do you have some evidence for that? Because far as I understand Xtra mod supposedly improves the AI.

And IMO original game has issues with too low quantity - at least the research "tree" is too scarce.

So why should I need a mod where I dislike and turn off most of things that mod introduce? :) No, I haven't had much time to witness it personally, just because I uninstalled XD earlier :) So it is more a question than a statement from my part: how does AI manage in this mod (mods). I just base on my previous experience with big complex 4X games that have mods. Modding AI in such games is a most difficult task in modding as far as I can guess (at least modding it in better way :P). Yes, I tend to agree with you here. Although this feeling of 'scarcity' of research in FELH seems to be more psychological (perceptive) than having the real impact on gameplay. As for me, I always play on huge maps, with abundant resources, plenty of quests, many of monsters and random events - but leaving Research pace and Magic power on Normal. And I can't remember any game where I'd seen that whether I or AI have no more techs to research and just loitering about knowing not what to do :)
The same could be said about troops/units equipment (derivative from Research though) - seeming rather modest if not scarce in quantity and variety, in fact I think there's just the exact quantity and variety of regular (researchable) equipment in FELH to keep things balanced and not overblown. Maybe, of course, it's just me :)

Well, while I meant a slightly different thing: if an author of a mod includes an option to turn off most (if not any) of the changes this mod does in game, it means not only that this author cares for potential mod users but also that this author considers these changes controversial, ambivalent or not necessarily improving the base gameplay. At least it's just how I see this. I'm not assuming AI works wrong (be it due to mod stuff or whatever else). I just have experienced many times that AI doesn't handle the stuff that mods added noticeably good. In some especially grave cases it ignores it completely :)
Though Stardock is known for having problems with real AI performance while bragging its 'human-like' and 'fiendishly clever' behavior (yes, I look at you, Galactic Civilizations 2), I wouldn't say I noticed any glaring AI flaws in FELH so far.

One thing you need to keep in mind though is that XD wasn't ever meant to be a single mod, it's a collection of more than a dozen smaller mod. Some of them were difficult to get working together so the author collected them together but that doesn't mean they're all supposed to be used at the same time. It just took away the hassle of trying to figure out how to make them play nicely together.