I'm going to try to do this by bolding the stuff I'm replying to...
Hela marches her army of dishonored dead and has a battle at Bourne Woods, in Nornheim (or else it is the Vanir or a coalition)
Yes, or the Vanir, but I dont think as a coalition is likely with the Vanir. I think they would be smarter than that. But maybe.
We should all thank Tom Hiddleston by the way, since, god of mischief that he is,
he actually let something pretty telling loose in that last video interview when he said while Loki and Thor are away that "for all intents and purposes Hell broke loose"...
Hell broke loose, indeed...
what's interesting too is from this quote it would seem that Hela may make her intentions known right at the beginning of the movie.
Meanwhile, the Naglfar crashes into Karnilla's palace (or some other small palace).
Yes, could be Odin's but I'm a bit skeptical of that.
The assault at Bourne Woods presumably is unsuccessful, thwarted by Thor, Sif, Warriors Three, and various other Asgardians.
Don't know yet. The videos I watched made it seem like they were being overpowered, so they may lose ground. My thought is that if it's Hela's army they may be triumphant in the outskirts, making their way to Odin's palace and surrounding it.
The dark elves are allied with Hela, and we need a McGuffin yet (if we don't want to use the ones offered by Andrew Lawden) to get Thor down to Svartalfheim to battle Algrim. We also need a McGuffin to get Jane into a scene with Odin. The dark elves might attack Midgard, but it's not clear what the motive is.
I am still thinking on this stuff, not ready to propose anything quite yet. I'll let you know when I do.
Surtur is manipulating things behind the scenes. Likely he is working through Hela. Surtur changes Algrim into Kurse, perhaps indirectly.
Hela sees this as a chance to gather more souls. Malekith sees this as a moment of power vacuum, with Odin's power waning. Surtur sees this as a chance to get back at Odin for the clash they had millenia ago.
Probably if Surtur is in it. I might add to Malekith's motivations may be linked to being "vengeful" over whoever messed him to to be half dead (or whatever). If it's more of a vendetta against Thor, than Odin, then that could be why he goes for Jane and Midgard. But we know there will be at least one Adewale x Renee x Anthony scene, per the actor, so hm... it could be a past scene showing how Malekith got messed up, and could still be Thor that does it but mom and dad come in to stop Malekith from killing him. (YAY to the idea of some young Thor and/or Loki flashbacks!)
<more plot we haven't figured out yet that brings Thor and Kurse together. Also, Tyr shows up.>
<Alice Krige does something. I guess the most likely idea is as Hela.>
<something happens at Stonehenge. Maybe a portal to Alfheim, maybe to Svartalfheim?>
This stuff, totally a guess but I suspect Tyr will be dead and leading an army either from Valallah or helping Hela. Based on the "first born" line in Thor 1, I suspect that Tyr will not be Thor's brother, but will in fact either be Odin's brother (which then would parallel the relationship between Thor and Loki) or no relation at all. There is an Einherjar Captain listed who will probably be a speaking part, and probably leading the dead good warriors, so I am beginning to wonder if Tyr could be working with Hela as her lead man. I didn't spy him in the Bourne woods scenes though but a lot of people were there.
Alice Krige as Hela, hella yes! LOL more than likely, and I'm very excited at the prospect that she could conceivably be Loki's mother instead of being his daughter. Will be some great dynamics here.
Come to think of it, where does Frigga likely go if she dies early in the film? Valhallah or Hel?
Stonehendge: yes, either of those, or simply a setting for one of those realms and not meant to be Stonehendge at all (just meant to make us wonder where Stonehendge came from, maybe...)
Perhaps Thor decides not to live in Asgard at the end of the film. (Avengers Tower is an obvious housing choice.)
Yup. Other than the frequent loud parties and frequent alien attacks, I bet it's like paradise!