Could the souls of Warforged be Quori?

I’m trying to develop a 5th edition D&D campaign set in Eberron. I know that the cause of the day of Mourning is open to interpretation, but I would like to relate the cause to the Dreaming Dark. I would like to ask for some ideas about Magitech for transporting Quori to Eberron from Dal Qour, and placing them inside of warforged. Would this make sense canonically?

Can a Night Hag catch souls without Nightmare Haunting?

Every night hag possesses a Soul Bag which is described as follows (cf. MM, p.178).

Soul Bag: When an evil humanoid dies as a result of a night hag’s Nightmare Haunting, the hag catches the soul in this black sack made of stitched flesh. A soul bag can hold only one evil soul at a time, and only the night hag who crafted the bag can catch a soul with it. Crafting a soul bag takes 7 days and a humanoid sacrifice (whose flesh is used to make the bag).

I was wondering if a night hag can capture evil souls only through their Nightmare Haunting or if they know how to do so when any evil character dies in front of them for whatever reason.

What is the complete lifecycle of souls in the Nine Hells?

The Descent into Avernus adventure provides more information about what happens to souls in the Nine Hells/Baator than was previously available (soul coins and their uses, in particular).

It’s also made it clear that I really don’t understand the paths that souls in the Hells can follow, and thus don’t feel able to convey the moral/logistical implications of any particular action relating to souls to players.

I’m looking for a complete picture of the soul lifecycle in the Hells (and I’m not expecting it to be linear). I could ask a bunch of smaller questions, but that wouldn’t actually help me understand the lifecycle as a whole so I can reason about it in unusual situations.

Answers should probably include:

  • States such as: being a living lawful evil mortal who hasn’t made a devilish pact, being a living mortal who has sold their soul, being a lemure, being in the River Styx, being tortured to draw out soul energy, being a higher rank devil, being trapped in a soul coin
  • Transitions such as: dying, being forged into a soul coin, being utterly annihilated, being freed from a soul coin, being promoted, being demoted
  • How the states and transitions relate to each other

5e materials & designer statements should take precedence, but materials from earlier editions are welcome in answers.

Can Favored Souls choose feats that require cleric levels, such as Initiate of Astilabor?

The Initiate of Astilabor feat (Dragon Magic, p. 20) has the following prequisites:

Prerequisite: Cleric level 3rd, dragonblood subtype, deity Astilabor.

As a Dracolyte silverbrow human having an innate connection with the Deity Astilabor, I would find it absurd that I could not take such a feat. I guess giving new spells to Favored Soul might be the reason why I can’t, but if Knowstones are allowed, why not this?

Is there any RAW info on this, FAQ, or Errata? (Pathfinder or other editions are welcome if that’s the only info available.)

Does a Nabassu benefit from devouring multiple souls or just from the strongest creature it devours?

If a Nabassu (Mordenkainen’s Tome of Foes) were to use its Devour Soul feature:

A nabassu can eat the soul of a creature it has killed within the last hour, provided that creature is neither a construct nor an undead. The devouring requires the nabassu to be within 5 feet of the corpse for at least 10 minutes, after which it gains a number of Hit Dice (d8s) equal to half the creature’s number of Hit Dice. Roll those dice, and increase the nabassu’s hit points by the numbers rolled. For every 4 Hit Dice the nabassu gains in this way, its attacks deal an extra 3 (1d6) damage on a hit. The nabassu retains these benefits for 6 days. A creature devoured by a nabassu can be restored to life only by a wish spell.

Can it only increase it’s hit dice once from the strongest creature it has devoured or does the effect trigger repeatedly for multiple creatures? (i.e. does it stack for each 2+ hit dice creature it uses this feature on)

Do all creatures have souls?

The term “soul”, despite being widely used, isn’t well defined in 5e. Do all living creatures have souls, or having a soul is a characteristic of specific types of creatures?

The only hint I’ve found so far is from the Mordenkainen’s Tome of Foes:

A nabassu can eat the soul of a creature it has killed within the last hour, provided that creature is neither a construct nor an undead.

Also inspired by this question: Where does an unaligned creature's soul go after death?

Do warforged have souls?

Page 8 of the B codex of Unearthed Arcana says:

Although they are constructs, they have much in common with living creatures, including emotions and social bonds, and perhaps even souls.

This last part troubles me however.

Do warforged canonically have souls?

Does Unearthed Arcana render Favored Souls redundant?

In Unearthed Arcana, there is a set of optional rules for Spontaneous Divine Casters. Under the assumption that these rules are used and that any Favored Soul fluff is ignored, is there any mechanical reason to play a Favored Soul instead of a Spontaneous Divine Caster Cleric? After all, the Favored Soul lacks some fantastic Cleric abilities like Turn Undead.