There's nothing I like more than a discussion/debate with someone that's in a polite manner, so thank you too.
1)This is partially backed up actually. Since, if the fifth soul that enters the safe room belongs to the Golden Freddy suit, and since we never see Golden Freddy being destroyed, that could mean that they are able to detach themselves from their suits. I'd wonder why they wouldn't move on if they can detach themselves, but it's most likely the "unfinished business"/"revenge" trope that truly keeps them attached.
This also means though that since there were 5 spirits in that room and one belonged to Golden Freddy, that the Puppet was not a witness in that room and is most likely, as MatPat showed at one point with the reflection, alive and perhaps, still vengeful. So we may see him in FNaF 4...
2)That's possible. It's just something I can't back up with evidence. But it is possible. I can try though to analyze it deeper though. and be aware that all of this is easily waveable since these are atari styled mini-games that heed little info as it is. Ok, so with that said, only 5 ghost appear, so that could imply he only feels guilt for 5 of the children. But as I said earlier, he killed 6 at least (unless you believe the Pink guy Purple guy theory) Freddy, Chica, Bonnie, Foxy, and Golden Freddy, along with the first child at the supposed diner, the Puppet. But all of this could be brushed off as a "graphical choice" or that Purple guy just forgot he killed that kid at the diner because that was like 20+ years ago... Meaning and I just thought about this, the purple guy is actually really old if he was at the diner, prob at his latest 16+ (but more likely 20+) when he killed that child (puppet) and Phone guy says that the diner has been closed for years, along with his statement that "If I had to sing those same stupid songs for 20 years" and we don't even know if he means 20 since Fazbears entertainment or the diner so that could mean even more, meaning the Purple guy is most likely 40-50+ in these mini-games if not way more.
3)I may have misunderstood you here, but if you mean that we were the childs spirit the entire time (for the mini-game), and the costume was so we could basically attach a name to a face. Then why do they get an error when attempting to go into the safe room? The reason as animatronics given usually is that they can't because it isn't on their image maps. But, if it helps, I don't know how true that is. Springtrap is able to walk around Fazbears Fright without any image map of the place unless Phone dude programmed it in him. But if he did, I don't know how he didn't notice the giant decaying head when he opened it up along with various other decaying bits.
Metaphor: I think he knows somethings up with the animatronics. Even if he didn't actually destroy the animatronics physically in the prior scene, there's still no reason he would fear and "destroy" certain animatronics and not Springtraps. It would make sense to destroy Springtrap's too, especially since it's the easiest one in his reach to destroy. But he knew Springtrap's wasn't possessed, or, at least that there was nothing wrong with it.
Literal:I brought this up partially as well in my "EDIT". Yes, that would make sense. If a child was afraid of Jason Voorhees you wouldn't need to look exactly like him, you'd just need the hockey mask and perhaps a machete to trigger a reaction. Heck, maybe Purple guy also laughed when he killed them the first time too.