Ok so first of all, from the research I did (which, admittedly, wasn't hugely extensive, but not nothing either), there is no one version of what the Nazis had planned for the east border-wise. When the Reichskommissariats of Ukraine and Ostland were created, they were initially only in western Ukraine and the Baltic regions, but this is because everything east of that was still under military occupation. There are various concept maps that show the different divisions of the eastern colonies, some with those Reichskommissariats staying the same and a large Reichskommissariat Moskowien stretching all the way from the north to the caucasus, some with them being enlarged as the German advance progresses. To me, the latter seems more likely, especially as wikipedia at least states that Reichskommissariat Ukraine was extended east up to the Volga in late 1941, though this is uncited.Isn't Reichkommissariat Ukraine too big? I don't wanna be this person, but it was planned that Reichkommissariat Moskau/Moskowien would occupy the rest of European Russia along the AA Line. And it looks like the Soviet Union collapsed into several States following the defeat.
As for the German Civil War, I don't really see a reason on why Himmler would start a rebellion, but it's up to you (I'll read the Reddit Post though). The SS is Hitler's loyal wing of troopers. Unless they wanted to take over the Army like the SA did in the 30s. Overall, pretty good though, and it's quite suprising on how Hitler's most trusted man in the SS would betray him.
And woah Partisans are everywhere.
As already stated, originally the idea was that Hitler dies, Goering comes to power, and Himmler launches a coup attempt. That may still remain the case, but I have deliberately left the events of the German civil war vague in recent times and I intent to at some point go back through and redo it, retconning some stuff, and perhaps bring it more in line with the kind of thing that can happen in the HOI4 mod.