In #3, Bo5A, Gandalf says Sauron put people after Thorin. This is a weak and insufficient explanation.
First, wasn’t that established when Gandalf found the contract on Thorin written in the Black Speech? Which happened before Gandalf asked Thorin who he told, meaning Gandalf already knew of the contract. Are a bunch of Black-Speech Speakers running around, putting hits on dwarves, such that big G doesn’t know which one it might be?
Second, how does Sauron know the specifics of when exactly Thorin is leaving the Blue Mountains and Shire? Or is Azog just hanging out in waiting? If Sauron is using his vision powers to look for dwarves, why can’t he do that looking for hobbits with rings o’ power later?
Third, the whole bit of the mountain’s strategic importance is dumped with the exposition stick. No build up, little discussion. Legolas and Tauriel do make it from Erebor to Gundabad in a day (or possibly a little more because the timeline is unclear), and they definitely make it back in a day, so Erebor must be on the cusp of Gundabad. But Gundabad’s in the Misty Mountains, which is several days travel by the forest road.
Even for elves going swiftly Hold on, the army of orcs from Gundabad makes it in less than a day to show up for the battle. And they’re travelling by day again, though they set out at night. Same for the Dol Guldur orcs, which are explicitly shown moving during the day. How is any of this possible?
The whole strategic timeline and geospatial positioning is a mess. And maps are one of the main things that make Middle Earth so interesting. Tolkien did the research, mapped it out, and for the movies to casually discard that is deeply frustrating.
The third point is utterly unnecessary anyway. Sauron should have needed the dragon horde to pay his mercenaries, which would have supported the money-bad(bad!) subplot.
How did Smaug figure out Thorin was called Oakenshield? Wasn’t the dragon sleeping all through that?
Tolkien did get fuzzy with the location of Thangrodim, so if I allow Gundabad a locational-superposition of any place with the badness, it could work. BTW, this is why Fonstad’s The Atlas of Middle Earth is so nice. Her maps are wonderful.