1. Root, I think your numbers might be off, or at least odd. VD has 8 legions, not 9? It seems like you're not counting the Scars, but only half of them turned traitor, so shouldn't there still be 9?
Also, (10 * numberOfLegions) fellowships total, each usually being a former chapter? Canon gives the number of loyalist chapters toward the end of M41 as ~1000, split across 9 former legions. The average fellowship would have to be the equivalent of ~11 former chapters to make the numbers work, unless there was an offscreen purge of 90% of Space Marine chapters.
2. I appreciated Subutai. And Guilliman as loyal to VD is amusing and appropriate. In my mind, he sounds like Indrick Boreale's voice actor.
Anyway, this is an interesting choice. I don't think we have enough boyz to take on the PDF, the Fists, the Guilliman-led Ultramarines, the Scars, and Doombreed's warband put together. The Scars have already sunk considerable resources into building our Waaagh! into a nuisance for VD, although (a) trusting Traitor Marines as allies seems dangerous and (b) that decision came from Subutai; Doombreed may decide differently once he assumes command.
While it doesn't make a ton of sense strategically to help the soon-to-be-stronger humie faction kill off the soon-to-be-weaker one, talking like that makes me sound like sum posh git who spends too much time thinkin' and not enuff time winnin'. Humie boyz don't get harder than primarchs, and primarchs don't get harder than the blue git, so having his 'ead for our pointy stick iz gonna make it righter 'n' properer. Thus, C.