I did just rewatch FotR and there is a shot of the dwarves with their rings in the prologue with explicit voiceover mentioning them. I think there is a reason we don't know what happened to Thrain in the movie yet, and I do think Gandalf is going to find him in Dol Guldur, but I don't see any reason to suspect that they'd deviate from that plot point.

I think, again just having watched FotR, that part of the point of Boromir for PJ is how similar he and Aragorn are and aren't. So, I don't think the parallels I thought were there in this movie preclude Thorin's canonical eventual downfall. Which, to be honest, I remembered more as being due to pride than to the Arkenstone; I deliberately haven't yet reread The Hobbit. But, I think seeing parallels with Boromir based on Thorin in this movie is completely legitimate too.

I think the moment PJ decided to give this book the trilogy treatment moments like Bilbo charging the Orcs became inevitable. I agree that it's ludicrous, but frankly I think the rabbit sleigh is more ludicrous.

I need to reread the Appendices etc for what they say about the Witch-King. If memory serves they never say that he was dead in the movie, just that he was buried after Angmar fell--which may well be canonical, because part of the point of the Witch-King is that he can travel bodyless to some extent. I knew the Azog vengeance whatnot was made up for manpain, though, sigh.