The Screens folder in the Documents subs always remains empty as dxpack files are moved/copied to the core (local) folder.
You are correct that if one does the steps outlined in "H1. (UI\Optional) - XW_1920x1080_Primal", one can skip section "H10. (UI) - XW_UnitDetailsWnd"
There are 41 Sovereigns, but the original ChooseSovereignWnd.dxpack only shows the first 10 using 2x5 columns (and then you can scroll down to see the rest). The modded ChooseSovereignWnd.dxpack shows the first 21 using 3x7 columns (and then you can scroll down to see the rest).
Black Market Bazaar 2.1 and XtraDeconstruct 2.0.p. are only compatible w/ FELH 2.0. Champion Bonanza is for the most part, version agnostic. Children of Storm 1.8.c. is compatible w/ FELH 1.8, but it's playable w/ FELH 2.0 (Additionally, I've done some work through XtraDeconstruct files to make Children of Storm fully compatible w/ FELH 2.0). In summary, the BMB+CB+CoS+χD package is fully compatible w/ FELH 2.0.
Finally, the dxpack issue is, indeed, only cosmetic and if you can live with it you can live with it, but it should also be easy to fix (Cut & Paste) and I'm really not sure what's wrong here. However, I'm more concerned about other issues; step 2. of "A1. (XtraDeconstruct) - Full Download Installation Instructions" has you moving XML files to the Program Files folder and the mod won't work properly if the files aren't moved to the right folder. What I mean by that, is if the dxpack files you moved aren't doing anything, then I suspect the XML files you moved in step 2. aren't doing anything either. If that's the case, the mod won't work properly... So it's my turn to ask questions:
1. Is your FELH installed in the default folder?
C:\Program Files (x86)\Steam\steamapps\common\FE Legendary Heroes\
2. How many dxpack files do you have in the screens folder?
C:\Program Files (x86)\Steam\steamapps\common\FE Legendary Heroes\screens\
3. In the screens folder (see above reference), (a.) delete ChooseSovereignWnd.dxpack , (b.) then start FELH, (c.) then click "New Game". What do you see? (Alt-F4 if needed).