For the first three points:The Black Workshop (The Gnomes) was originally one of the Society's Thirteen Factories. However Osbourne usurped control of them after the Liberl Incident, because they had the same goal in mind, the completion of the Sept-Terrion of Steel, by invoking the Great Twilight. Vita's Phantasmal Blaze plan was an alternate attempt to try and seize control of the Sept-Terrion without invoking the Great Twilight, but it failed. The Anguis' of Ouroboros want the Sept-terrions for some reason, and they decided that getting them was worth the risk of ending the world, and outvoted Vita 6-1 in that regard.
Point 4 is covered pretty well by Shadow Dino. Question 5 and 6 is straight up Cold Steel 4 Spoilers so I can't say much about it.
As for point 7... The Great One (Sept-Terrion of Steel) is actively working toward a state where it can be revived. In order to do so, it needed the cursed divine beast to die in order to return to it's true form. The mechanism of this revival was written in the black records. We can assume from dialogue that the events can be changed to an extent (see Osbourne talking about forcing the Civil War to happen ahead of schedule), but that they will happen eventually, in some manner. So the great power is manipulating people and things to make it revival happen, by acting like the devil on the proverbial shoulder, whispering in their ear.
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Spare me your obsolete empathy The voice of sympathy means nothing to me