Maybe a dumb question, but how can you tell if a pentacle necklace is upside down?  Yes, supposedly there is an up side and a down side to a five pointed star, but the necklace might be different.  I think the center of the picture is too fuzzy to tell whether or not the ruby is there or not.

In the beginning of Small Favor he has a bit where he explains some of the Pentacle lore to Murphy and talks about the first point being the Pentacle's North (or something to that effect) and that the first line you draw plays a role in that, but the way he described it sure implied that the "normal" version has a point facing upward.  In most of the other covers I can find good images of at the moment (Cold Days and White Night right now) it has that more normal/traditional point-upward orientation, but in both Peace Talks and Battle Grounds it's point-down.

The prisoner would speak the language he spoke just before he was locked up. He told us he had to be locked up so that reeks like a Lea scenario. Infected, able to fight it but not able to keep it under control all the time. Knew about demonreach and decided to have himself locked up.

Agreed, i too got the sense of a voluntary committal more than a traditional imprisonment.  Im leaning toward it being a former Warden that used too much Black Magic but is cognizant of the fact that he is Tainted and untrustworthy.

Charity telling Harry to stay in the Hospital, that Family would stay

I suppose the whole etherealists go insane thing is conceivable as a mutation of the law that DV magic has drawbacks but what specific form they take shifts slowly over time.

Maybe, but the fact that the energy in question affects Everyone to the point of requiring goggles Or Else makes me think that they are less the source of it and more of an evolutionary adaptation to it. 

In fact my own pet theory is that Folly is not actually Damaged/Insane the way the rest of the etherealists are, but rather she was born with an atypical brain (autism spectrum style) that naturally adapted and is letting her be an etherealist without accumulating the brain damage they normally would.  I think this is why the "Enemy' wasnt able to find any purchase in her brain, there were no unnatural "holes"

I wanna see Rudy in a looney bin with Harry taking a few moments to mess with him. But, that is the sadist in me.

Id be open to a mild redemption arc where Harry turns a corner and discovers that he finally had the CranioRectal Extraction procedure and is now volunteering at the BFS, doing something entirely non-threatening like Day-care.

A supernatural effect keeping adults from sensing them right then and there maybe. There doesn't appear to be one keeping adults who hear about them as adults from remembering from that point.
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It does make people forget as they age though, and we dont know whether adults are capable of retaining the memories. If they could remember then it would not have fallen out the way it did in the Carpenter household because they (the carpenter children) would have been able to just tell their clued in parents rather than having to go it alone and make a secret slayer's guide. 

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Because, again: Harry knew about the bogeyman.

Which is pretty decent evidence that the Bogeyman not a race of Creeper. There are tons of phobophage species out there, just because that one is classically associated with children doesnt make it one of these things. 

The English accent is obviously(at least to me) signaling something. But what? Could the guy have been the last warden? Is the backstory related to the Gatekeeper and the and Demonreach's limp?  Maybe the Well has been attacked by the outsiders before, maybe in the same way that Winter was attacked through Lea.

Worth noting that the entire conversation, including the accent, were happening in Harry's head, so the accent could be literal, or it equally could be part of harry's mind interpreting the communication in a familiar way (though the Piss Off slang makes me think it would have to be at least a little bit two-way. 

I think you guys are overselling the "adults don't know" thing.

I really don't think it's that adults are incapable of retaining information on them. Just that they can't normally perceive them, so they forget or rationalize away what happened to them as kids when they grow up.

That happens with totally mundane things. There were games you made up with your friends and played as a three year old that, in the moment, you knew forward and backward, but a few years later you don't remember it even happened.

Again, Harry was well aware of the bogeyman, even though that's the same kind of thing as the haunts and the creepers.

Nope, it's very much a supernatural effect.  Keep in mind that the very authors of that book, the carpenter kids themselves who are entirely aware of the Adult supernatural world, are also forgetting these things as they grow up and pass the book along.  The fact that Mouse has difficulty sensing them also proves there is a supernatural effect at work.  Id have to go digging but Im pretty sure this was even confirmed in one of the older WOJ's when he was first talking about the Zoo Day concept.