AOVS / Render Compositing questions- Volume, Explosions,Matte

Hey there, having a couple of AOVs / render related questions.

1. Are there any aovs for compositing explosions? Like for the fire / emission / volume to seperate them and bring them back together in Nuke afterwards?
2. I have a planet with some cloud atmosphere and I want to render the clouds seperatly for comp. How would I go about only rendering the clouds but have the effect of the planet so the light does not go through the clouds?
3. How can i exclude objects from the final render but keep only their shadows.
4. Is there a way to only render the light emission of an explosion affecting the scene without rendering the whole explosion?

I know its a lot of stuff but I tried searching the docs and could not finds answers.
Would be amazing if someone could help me out here!