Avernite - Yes, that is the true purpose of Faerie. Doesn't mean they don't have feuds and wars and other enemies. And you're assuming the Fomor are not connected to the Outsiders in some way. There is lots of supporting hints about the connections, and we know during this summit that Outsiders are summoned. And I think you fail to consider the consequences for Faerie should this Titaness succeed. She intends to reshape the mortal landscape. For a bunch of creatures who rely on mortals, you'd think they might be wary of that. Not to mention if she ends up freeing Outsiders/Old Ones etc. Also, when you talk of resources you're assuming Harry can actually kill a Titan. Unless it's on Halloween or a similar conjunction it isn't possible (as far as we know). But then there is the small matter of actually damaging her. She might not be so vulnerable to mortal weapons as the foes Harry has previously faced. Read her description again - she's above anything he's fought before. So the question become why wouldn't one or more of the Queens take the field to lead their forces? A Titan isn't a minor inconvenience. It's a major-league threat. Which means if they don't show they actively don't care for the loss of human life and reshaping of the world (which we know they do...to a point), or they are otherwise obstructed/distracted. My guess is an assault on the Outer Gates for Mab and Titania just won't show...which suggests certain things about her character and motives. There is a whole theory on Titania which makes sense about this.
Conspiracy Theorist - We don't actually know it's the Merlin who wishes to throw Harry out. It could just as easily be Cristos or even Mai. All the Senior Council know of his relationship to Demonreach, and are basically aware of what that means. I suspect other senior wizards would have similar knowledge. Especially some Wardens or those mysterious thugs working for Cristos. I assume by "super weapon arsenal" you are referring to his weapons of Christ? Also I can tell you now you don't need Soulfire to use them - why would Nic want them if he couldn't use them? The only thing needed is human will.
If Dresden did establish himself as a Freeholding Lord he would be playing right into the hands of the Black Council. Civil War is to be avoided at this stage, the Council is not yet the evil oppressor that needs to be opposed (although I suspect that is where the story will go assuming it survives the next conflict). I don't know where you are getting the idea that the Merlin doesn't know about what Demonreach is...it has been confirmed that the Senior Council all know about it and what it does. It is the White Council at large who is mostly unaware. And I am sure the Senior Council each know a bit about Harry's allies. At least two of them specialize in information gathering (Martha Liberty and Mai), Rashid seems to have more on the ball than most so it's safe to say he is at least aware of these events (especially as he seems to keep an eye on Dresden), if Cristos is black council I would expect him to have his own special resources in regards to information, Ebenezar knows definitely about Vadderung, the Merlin is at the top of an information gathering organisation (and is the most powerful wizard on the planet) so I wouldn't be surprised if he had the gist of what Harry has been up to. LtW is the only one I am not sure of but time will tell there. Harry won't release any of the creatures unless he is tricked or is somehow manipulated/forced to. Nemfection aside, they are just mean and horrible and all it would do is cause pain and misery to a whole bunch of people. And considering beings of the Naagloshii level are the least dangerous beings in there...it gives you an idea of just how bad that would be. And I think Dresden hasn't even found the inmate(s) in maximum security yet.
I highly doubt the spear is Zeus' thunderbolt. It's most likely his staff with the Spear of Destiny (or Spear of Longinus) attached as he literally just picked it up last book. As a second choice I would say it is Gungnir (Odin's spear) because of his relationship to Odin.
Mira - Yes, you are largely correct. They were imprisoned in the deepest and most terrible pit in the Greek Underworld, known as Tartarus. This was after the Olympian Gods defeated them in battle. Zeus' thunderbolt supposedly blew the top off their base of Mount Othyrs. But it took the combined might of Zeus, Poseidon and Hades to defeat their father Cronus/Kronos. Which puts in perspective just how strong these Titans are.
I can see how Harry might achieve it, but he still has to get the Titan to Demonreach. Which might not be so easy. Not to mention that his job is to kill the Titan, not imprison. I agree that I think when Harry finally does end up imprisoning whoever he will end up tapping that well of power.