Hey, XtraDeconstruct plus DLC Compatibility Files is the version you want for the Ultimate FELH GOG installation.

If, later on, you end up installing additional mods (Black Market Bazaar + Champion Bonanza + Children of Storm), then you would need to install additional compatibility files to make these mods compatible with XtraDeconstruct (Specifically, the following files: XD_MOD_BMB + XD_MOD_CB + XD_MOD_CoS).

To get the basic version of the mod installed and good to go, you only need to read the installation instructions (A1) and the Unit Details Window (H10) sections. If you want to play w/ custom factions some additional reading is required (M1).

Other sections allow you to customize your installation, expand the mod scope, do some modding yourself, or are tips/instructions on various subjects, but are generally not required.

As someone who was recently in the same position, I recommend starting with XtraDeconstruct plus the included interface improvements. Nothing else at first until you see how it works and what it's like.

Follow Primal Savage's instructions exactly, and you should be fine. It'll be a lot better than vanilla.

XtraDeconstruct 2.0k
[ Released 16 November 2016 ]

Update
It's now possible to play the Republic Government Mod (v1.6) w/ XtraDeconstruct.

Info (Stardock)
Download (Dropbox)

EDIT: Links removed (Now included w/ 2.0.m.).

XtraDeconstruct 2.0m
[ Released 14 December 2016 ]
[ Updated 21 December 2016 ]

XtraDeconstruct 2.0n
[ Released 16 January 2017 ]

This is one of the most stable version of XtraDeconstruct ever released; it's also the last.
I will no longer be monitoring this thread. If you need support post in my Stardock thread.

Enjoy!

Oh wow. Thanks for all the effort you put in to this Primal. Good job.

Thanks!

It appears I will need to update the mod at some point this week or next weekend because Black Market Bazaar has been updated to version 2.1. It will mostly be a compatibility update, but nonetheless an update I suppose.

So word of warning for newcomers, the current version of XtraDeconstruct: Legacy of Magic (2.0n) is compatible w/ Black Market Bazaar 2.0, do NOT use the 2.1 version.
[File: Black Market Bazaar compatible with - Children of Storm - XtraDeconstruct - and friends 2.0 which was uploaded at 17:13 on 22 December 2015]

Support has ended. See OP for information.

Probably a bug:

Blood_Halfdrake has 2x +18 initiative. And the XML code looks messed up there too.

Description for Halfdrake also has 2x +18 initiative.
Blood_Gorgon has 2x +18 initiative in the description but only has 1x +18 initiative.

Either bug in code or in description:

Inspiration spell description says +1 Research (same as base game) but the spell actually gives +2 Research (unlike base game). This is due to the '+1' in '<Expression><![CDATA[[UnitStat_SpellDamage_Order] + 1]]></Expression>'.

"Dynamo" weapon: the 'go next' part does not work. The .xml uses 'MeleeAppliesDefenseSpell' which is probably a bug and rather should be 'MeleeDefenseAppliesSpell' instead. (Though I dont know if it will work then.)

The .xml for <SpellDef InternalName="Spell_X_SummonLightbringer_2"> has 2 bugs:

<Calculate InternalName="Calc" ValueOwner="CastingUnit">
<Expression><![CDATA[[UnitOwner_GetNumLifeShards] + 5]]></Expression>
</Calculate>
<Calculate InternalName="Calc2" ValueOwner="CastingUnit">
<Expression><![CDATA[[Calc2] + [UnitStat_BonusSummonLevel]]]></Expression>

The (bolded) 'Calc2' needs to be 'Calc'.

And the description says '+6' but the .xml gives (or would give it wouldnt be bugged) +5. So the (bolded) '5' should probably be a '6' instead.