Quote Originally Posted by Cèsar de Quart View Post
BUT. I like that the Stormcasts are dead heroes reborn. It has potential. I don't know why they're fighting, or what they're fighting for, but I like the concept. So I thought: why no improve upon what's there, and fix them?
In short summary? You weren't far off with the Errant Order - Stormcast Eternals were literally mortal heroes (Bretonnia, Empire, Tilea, etc) which got magically pulled away at the moment of defeat/death to be transformed into fantasy Space Marines (with Celestial magic) and have returned to find a thousand years have passed and Chaos is lording over the ruins of their empires. Now they intend to take it back...

I personally find it's best to take inspiration from WHFB, but not directly copy it if I were making the background of my AoS army (it's just respectful to leave it be). Rather than outright saying these Stormcast are elevated Bretonnian Knights, maybe just "warriors of the ancient Kingdoms of Breton" and select weapon and equipment which make them excel at monster hunting, for example?

In regards to your questions: Yes, they Sigmarines can survive isolated from Azyrheim (Celestial Realm) but upon death, they discorporate and shoot off like a reverse lightning-bolt into the heavens and return to Sigmar to be "reforged". Yes they can rust. It tends to require a magical affliction (fighting Nurgle for example) since their equipment is inherently magical, but it can be coated in soot/ash, burned by Nurgle corrosive slimes, etc.

Can they disobey orders? Possibly, but I don't think Sigmar is very specific. As an example in one of the audio books where Stormcasts of the Hallowed Knights are seeking out Nagash to attempt to form an alliance, they find shelter with some human mortals who worship vampires, offering their blood in return for protection in a tomb-city in the Realm of Death... but a Chaos warband has been tracking them since a previous engagement, and the Stormcast choose to stay and defend the mortals (even if they find their behaviour repellant) when all tactical sense and their mission (reach Nagash) says they should press on and leave the humans to the Chaos warband and their fate.

Unlike Space Marines, they're essentially still "people" for the most part, and view the humans of the Realms as their lost and broken descendants.