Red: I prefer calling that process how we refine ideas.
It is out of character for the quest makers (at least mine) to have it so the group must rely on outsiders (regardless of how trust worthy they are). I would go as far as saying they wouldn't allow a section of the quest where the group needed outsiders. Why is that?
1. Well for starters these stages of the quest are test for the group. They are designed to see if the group posses certain virtues (that Red and I of deemed important) such as wisdom, courage, compassion, honesty etc.
2. Rremember that the group will not get the time matrix (Odin and the Norns knew about that) so these quest are preparing the group for a different challenge really.
3. The quest makers want the group to rely on each other and not outsiders.
4. The group must be able to face the minor dangers on Tarsis (no matter what you say, in the grand scheme of things they will be minor). As such the quest makers would most likely have the group go through the most dangerous parts of the planet. If they can't survive Tarsis by themselves then they won't be able to finish the remaining parts of the quest.
Another thing that is out of character for the group is to have them rely upon the Agamari *for anything*. Time has shown that the group doesn't bother to seek out local governments or try and get any help the exception being Midgard. Where one the planet was inhabited by the Aesir, and the group wasn't given much of a choice. This wont' be the case on Tarsis. Why? The Aesir and the rest of the group don't trust the Agamari.
As far as your scenario (about stumbling into a bloody war etc). The group would avoid getting themselves entangled in the war especially after losing twenty years. They would try and remain neutral and reach their objective as quickly as possible.
Also so far your locals don't seem all that dangerous, when compared to the skill/power the group possess even if they don't have things they rely on.
Something has just occured to me. The Agamari invaded Tarsis (still I'm not sure why), the original inhabitants could be/are just trying to get rid of the invaders and free their world. It is not a far step to say that the Agamari are the bad guys in this conflict with the original inhabitants the good guys. It is not even a stretch to see why they attack outsiders after such a bad experience with the Agamari.
If the Norns take that view point (I say if since I don't know the backstory) then they certainly would prevent any part of the quest involving the group relying on the Agamari. Speaking of which, keep in mind BD that the Norns are my characters and I have final say in what they know and who they share that knowledge with. Normally they do not share any information about the future or events.
Another thing to keep in the back of your head as you develope this plot line. You are essentially taking control of some of my characters and Reds. When we ask for reasons for a situation or argue about one, we are trying to make sure that this section of the quest remains true to what our characters (the quest makers) would do. And if we say that none of the quest makers would do that you are going to have to take our word for it since they are after all our characters (and in the past you have misjudged how at least my characters view certain situations).
So with that in mind I ask what is the purpose of going to the underworld? Is it a test of somekind and if so what is it testing (something to keep in mind the questmakers wouldn't restest virtues the group has already shown to posses)?
As far guides. Hal is certainly free to offer them to the group, but at least Odin and the Norns would not design a section of the quest where the group would need to have a guide.
I think that is everything I wanted to say.