Sometimes, I think we as fans forget that the entire story of Welcome Home is about the mystery behind a once beloved puppet show and why it was taken off air and essentially removed from public consciousness.
It's not really about the characters themselves and what they get up to in their fictional universe like we're used to. And I think the deeper we get the more obvious that becomes, especially when we are part of the Overall Story, we are not passive watchers occasional puzzle solvers, we are part of the Canon.
There are multiple sides we are seeing here as part of the Overall Story and the way each thread together is vital to understanding what the Actual Story is, if we take only one bit of it and especially if we focus too much on seeing everything as 'Canon To The Characters' we're gonna miss Clown's vision.
The first side we see through merch, looky-loos, the Darling broadcast etc. This is the 'lives' of the puppets, the Characters. This is the material that shows us how the Characters acted, sounded, interacted with each other, their relationships with each other etc. This is Character Canon.
The point of that stuff in the Overall Story is to make the fake show feel really real, as if it were something that actually existed and also to show us Clown's Vision of the characters.
When speaking of the Characters, this is really the only stuff we can trust to say actually 'happened' to them or more so...was written and acted out to be the canon. This is the stuff you should be talking about when discussing just the Characters who aren't (or shouldn't be) sentient/real.
So things like there being a narrator aren't that important because well, it's just a pretend story, of course it can have a narrator that interacts with the Characters etc, of course they shill their merch and talk to the audience. They're people acting as fictional characters.
Side two are hidden snippets of the lives of the Real People who worked on the show in some way.
These are being shown to us through visuals of the puppets, sure, but it's not Character Canon.
(One could argue that someone is drawing the characters in place of the Real People on purpose to match recordings they somehow have from...the 70s...when this happened...look you have to suspend a little disbelief because they include elements like Eddie having an ear piercing that the puppet doesn't and clothing changes we've never seen the Characters in which were probably Person Canon which would indicate that the artist saw or knew them...but who knows).
Person Canon tells us what was happening behind the scenes. It shows us how the people behind the show interacted, what they thought of each other, the relationships they had ('Eddie' and 'Sally' are friends! 'Sally' likes 'Poppy'! 'Eddie' and 'Frank' had a thing that 'Frank' apparently broke off and perhaps regrets!), the things they did (e.g. Poppy the person smokes weed but not Poppy the puppet who can't because she's not real) and lets us glimpse into how the show was run and maybe in the future what happened to it.
The hidden letters are clearly from these Real People, speaking about things like the Frank Puppets being created and the workings of the show.
The third side is a potential crossing between Character and Person which is happening in the Overall Canon.
Frank seemed to experience his costume being tailored by Eddie as they got ready for Sally's play (something that absolutely could happen in Character Canon), but we then learnt it was Eddie (the real person) who tailored ('Frank' the persons) puppet.
Julie and the flower - which once more seems in line with what would/could happen to the Character but hints at something else being really true and having actually happened to the Person perhaps, or some kind of mix.
Poppy (the person) having an anxiety attack about something that didn't really happen to her it was happening to the puppet (I can't tell whether it's supposed to have happened to the physical puppet or was just written for the audio book or both).
Eddies dissociation where it flashed between 'drawn' and 'real' twice, one time in which he seemed to not be in control of himself. He says he gets 'headaches' before this comes on - is this caused by the merging of the real self with the puppet character? If so how? That's the mystery of this side of the story.
I'm probably missing more examples.
The fourth side is the parts that are aimed at us. They are not part of the pretend show, they are not old recordings of real people from the 70s. It's happening here and now.
The communication from Wally who seems to be...real? Or, linking to the third side I mentioned, might be some mixture of the Character and the Real Person. He clearly exists in our current time and is talking to us here and now but might not fully be in our reality which he really wants to be.
The communication from 'W' who is the one getting this merch and updating the site in the Overall Canon and who seems to be having strange experiences because of it is also part of this fourth side (because 'W' is not Clown, in the Overall Story, Clown and everyone else involved are not involved in this at all). They are the ones who told us about Welcome Home. They are the ones inviting us to relive the show but they are not the ones who are showing us recordings of the Real People and what happened to them or changing the site to add puzzles which they don't understand either. That is most likely Wally.
There's also the mystery of Ron, who we know is the before named creator Ronald Dorelaine but who does not have a puppet named after him (if it is true that the people and puppets share names) and aside from being mentioned by the Real People we haven't heard anything from him.
Going forth I think it's vital we're able to understand which side of the story we're experiencing, that'll help us put together whatever the heck happened to those people back then and what is happening to W, Wally and us now.