That is true, the Little Folk are everywhere. Yet, the further they are from a commander, the more likely they are to forget their orders. In the same city as Harry is one thing, but all over the planet is quite another. Toot-Toot is their general, and even near Harry has trouble with orders from time to time.
Lots of people wear iron, or rather steel. Rings, bracelets, other paraphenalia are not uncommon to wizards either. But as you say, it would need to touch them. As you point out, many wizards wear warded/enchanted clothing too - which they also would have to get through. I acknowledge that some wizards caught out in the open, unprepared, would be likely to be in danger - if the Little Folk remembered to follow up on their orders.
When you say, "engineer a breach of the accords" what do you mean? I can't see the Mother's being at all involved, as they really don't do much at the local level. Titania or Mab could be involved, although only Mab enforces the Accords as they are her Accords after all. Titania, on the other hand, exists to counter Mab against humans. If Mab really did approve such a thing, Titania would likely involve herself to stop Mab. So at the very least half the Little Folk wouldn't obey such an order. The other half, the Winter-aligned half, might come into direct contention with the Summer-aligned Little Folk at this stage.
Are the White Council on the out with every member of the Accords? Where did you get that idea?
Christos may or may not be dead - his status is unconfirmed. But you forget Martha Liberty (the communications and intelligence expert, also the spirit messenger expert, on the Council) also witnessed Harry's display. She almost certainly would have informed the Merlin. Not to mention, the White Council don't necessarily need to be physically present at events to view them or learn about them. They can scry, remote view, ask spirits and other allies, and probably a number of other intelligence avenues.
Would releasing and then controlling Ethniu be easy? Considering how hard it was to put her away...I don't think so. Let alone giving her a superweapon. The WOJ states Harry could use Ethniu, not that it would be easy. Not to mention, he would have to force her to kill the Council, because why would she willingly help her jailer? Honestly, even if Harry could control the Naagloshii and were crazy enough to send them, I very much doubt they would get through the threshold and wards on Edinburgh, not to mention they lose power the further and longer they are away from their hunting ground.
I mean, we don't know whether the White Council know about the Arma Christi or not. But I don't think it's unreasonable, considering Harry whipped out two in the Battle of Chicago, not to mention the Underworld heist wasn't exactly quiet. It's not like they wouldn't know about them, this isn't the first time since Christ they have been used. They are weapons after all. Hades was just the caretaker. Do you know that Mab, Odin and Hades are keeping events secret? I don't remember anything about that myself. And why would they? They wanted the news of Skin Game to be public after all, it was return fire for Mab. Marcon may or may not have known about what Harry got, but it hardly matters. Namshiel would have known where they were anyway, and so Marcone would have been able to put 2+2 together. I guarantee that little heist was at least decades in the making. Nicodemus doesn't do things on a whim. Which means Namshiel would have been privy to some of the plan anyway. I imagine Marcone was surprised that Harry actually had the Spear/Athame with him when Harry produced it in the fight with Ethniu, but I wouldn't be so sure Marcone didn't suspect Harry had already retrieved it. It was that Harry had it with him in the moment that surprised him, I suspect.
I think you're overestimating the Archive there. The Archive knows anything written or recorded, sure. But the crystal is memory in physical form. That's not at all the same thing. Not that the Archive would care, I am sure it has plenty of it's own research and knowledge about Ways. But I would be very surprised if the Archive knew exactly what information the crystal has. I am surprised to hear you think it would be so easy to duplicate? When has any type of magic been easy, even for Harry? There are passages over and over about how hard it is to do even simple things, let alone complex magic. It's not a matter of inscribing the gem, runes are not the issue. It's the transfer of the information, the copying of it. That might literally be beyond Harry. He's not all that good at the subtle and complex stuff as it is.
I am not sure I understand where Mab is needed, or for what, when it comes to the gem...?
The Fae work to the letter of the law, not the spirit. Which is clear from how they often get the better end of the stick. Butter's didn't save Mab's life, he literally just pulled out some iron that was paralysing her. At that stage, it wasn't killing her, least as I understood it. But even if the Fae view it the way you do, I doubt he can ask for anything he likes. Mab is only one part of Winter. He didn't save all of Winter, that would be conjecture.
I think the one thing that is clearest (sadly) from Battle Ground is even in the face of irrefutable evidence, Harry's world just ignore the supernatural or try and explain it away. Despite a god literally showing up with an army of monsters of myth, and a second army of mythical beings showing up to stop them, humanity blames "terrorism" on the Battle of Chicago. Harry could crow from the highest hill that he is a wizard and he would blend in with all the other crazies. Consider what he says at the end of Changes, words to the same effect.
At the end of the day, Harry's life is never so easy that he could simply defeat his problems so simply. If the White Council were so easy to deal with they wouldn't be around now. If Harry were able to convince people of magic so easily, he would have. But Harry's life never goes that well. Not to mention, Harry's reputation publicly (even outside the supernatural world) is mostly considered nuts and/or a dangerous criminal. He might have won the respect of some Chicagoans, but I imagine plenty will hate him just because of what he reminds them of. They will want to go back to the way things were, and will blame him for their troubles. It's often the way of things, and has happened to Harry many times over as it is.
Larry Fowler...might actually be supernatural himself. Jim has hinted at it. My bet is he is a werewolf (in the old Wolfman movie the werewolf is called Larry Talbot).
FYI - just going to split this thread as it might be easier to have the two separate topics, because I enjoy both but don't want to railroad discussion.