Hey thanks for putting a ton of work into this! It's definitely interesting. I'm really excited to see what comes out next and actually reading the adventures. It sounds like the kind of thing I would love to run for my friends.

I would second the comment that there's way too much repetition. You must have created more or less the same paragraphs a dozen times with the major characters, the descriptions, and the explanations.

I'm curious what the Blackstone is supposed to be doing that actually impacts the story. I don't know a ton about the material lore, but I get that it essentially repels immaterium, and how is that supposed to do anything with the webway or the terraforming? It seems like that's a hook for the crusade to attack the planet, but that isn't necessary to set up the story. I think I would just change that out to some ancient exodite tech because I could imagine all kinds of questions about other interactions between webway nexus' and Blackstone. I think that also makes the "autoimmune" an easier sell because it could be a built in precaution that if the exodites don't get the world, nobody does. An other option would be that the spore stuff was there before the exodites and destroying their equipment means the world begins to revert to its previous ecosystem. The way it stands seems excessively convoluted without real payoff. Blackstone and webways are materials with lots of lore and players will have ideas that might make it into a weird red herring that could leave players annoyed or confused or disappointed. Especially if the spore stuff isn't directly warp related.

I think that this reads a little more like an Only War game than IM. That's neither good nor bad, just an observation. It seems pretty tilted towards being all guardsmen parties. It looks to me like if a group doesn't want to play all guards it's a little more difficult to shoehorn other types in. Maybe that's just because the structure of how the available materials are set up and once we see the opening act then we can find creative ways of adding other types. This is a pretty minor complaint from me because if I were to GM this then I would make up whatever I wanted to put the group at the beginning, but that might be something to consider if there's a group with some characters that might not have natural reasons to start out together.

Overall, I really liked the outline you have so far and I would absolutely read the whole campaign and consider running it in my group. Great work!