This sounds almost like an exact solution to
my post here. Definitely giving it a try.
Early feedback: One small feature that seems to be missing is the ability to add a descriptor/label to actions.
Works pretty well otherwise though. I'm experimenting with the selection modifier so I don't have separate actions for AO3 and FFNet fics.
Also, I found it's helpful to add a Calibre Action to toggle mark on all the books before starting a chain, and then at the very end setting a search to marked:true.
A small suggestion: It might be a good idea to have a custom action to prompt for confirmation for more...destructive action chains, and pressing "no" would halt the entire thing. I guess this could be made with a module though I'm not sure how.