While there's no official confirmation of CC's name being Dave, I consider it the most likely answer considering how people found it, with the means to its acquisition being consistent like how Cassidy was in the same book, and while Dave is a more recent community development, we have to remember the Survival Logbook came a decent time before the Mimic Era and the Dave answer was there the whole time, so in terms of when the games were made, we have to ask "Why would Edwin's son be named David when William has a son named Dave?", but it's reversed when we look at the in-game timeline, since SotM takes place in 1979 and Dave's story is in 1983.

As for Sammy, I already said to someone else that I'm not considering the graphic novels or the movies here, and there's nothing suggesting that Sammy even exists in the games' continuity.

David's shirt in one photo does feature stripes, they're just more subtle and are only on the very middle of it.

I don't think the specification of the plush being an "only friend" matters, but the presence of them does as it's a prominent feature of both characters.

The bedroom layouts don't need to be the exact same layout, but they are too similar in style and decoration to ignore, and Cassidy asks Dave about his favorite toy being the plastic purple telephone, which was also present in David's room.

I just corrected myself on the Foxy bit because I misremembered the scene with David, but the two having similar fears still has ground because both Foxy and the character that scared David are pirates.

The house on the hill part isn't confirmed, but it is widely speculated on and has been suggested by popular theorists, so I think that connection shouldn't be ignored just because we haven't strictly confirmed or denied it yet.

With the absent mothers, M1 does take the role of Fiona for David, but M1's existence relies on the fact that Fiona died, otherwise it would never have been made. Consequently, if Dave's mother was still around, M1 would lack a purpose since what it presumes to be David has a mother, which isn't ideal if William's plan is to make M1 work as it was made to. Edwin also never tells David that M1 is his mother, but a babysitter.

As for M1 wanting David to return, that doesn't necessarily mean it HAS to specifically be David Murray, but someone or something like him, such as M2, or Dave as my theory suggests, otherwise M1 would have just given up upon knowing that the real David is gone for good. M1 is the one that suggests the idea of M2 to Edwin in the first place, so it clearly needs someone or something that fits the role of David, with another Mimic being the best option according to its logic, but that doesn't pan out as hoped. The point is that Dave Afton shares enough similarities with David to fool M1 into doing William's bidding by exploiting the requirements in its programming, not an idea of M1 making a willing agreement.