So this part...
...kinda changes everything about how I was seeing your story.
If this is where the story starts, rather than starting with the stealing of the prophecy as Mike suggested (note: the stealing of the prophecy can be the first driver even if it happens prior to the storytelling), then this changes what I see as the OS Goal and Concern. I could very well be wrong about this, though.
Anyway, if the OS Story starts with the stealing of the prophecy, then I see it as they have problems from trying to regain possession of the prophecy and have a goal of regaining possession of the prophecy. This is fine, but this is the kind of thing I see and start feeling like it's kind of bland. Not because it's bad, but it's just really straightforward. "We have problems from not being in possession of the prophecy so let's solve it by regaining possession of the prophecy." In this story, getting Luke's help might be a Requirement or Prerequisite, or just one of the Optionlock's or an SP.
It does seem like this problem could make the first story in the series seem pretty self contained, though, which could be a good thing. Like Star Wars: A New Hope. That story doesn't need anymore after it and doesn't necessarily leave me feeling like there's anything else needed in the story. But it does allow for the war to continue and for the world to really be opened up to the audience in the next chapter.
But if the OS story really starts with a decision to get Luke involved, then it changes things up a bit. First, it makes me think the OS problems come from trying to recruit (Obtain) Luke's help, but rather than changing the Goal to "having Luke on our side", the Goal could still be "regaining possession of the prophecy". This isn't as bland to me because it feels like another layer. It also seems like it could make this story feel like the first part of a larger series rather than a self-contained story about destroying the prophecy. Like, "we need to get Luke into the battle for Ragnarok, and we do that by showing him how he needs to help us fight against TDE, and after he succeeds at that, he will continue on in the fight to help us bring about Ragnarok". This might feel more like the first installment of The Lord of the Rings.
I like this, too. If the murders take place at the beginning of the act, it's like everyone is reacting to being murdered and the options look like the number of NGs still alive. If the murders are at the end of the act, then the good guys look more proactive and we see that each attempt to stop TDE is failing. Again, both are fine and I may be seeing it wrong, but just sharing my preference.
I could go on, but that's probably enough for now. And I may be wrong about all that, anyway.