This was very helpful and all sounds very reasonable to me.
I was thinking of having Castiel be settled at the start because 1)He's used to knowing more about situations that his humans and 2)Time travel is really no big to him. It'll still be weird to suddenly be in a carnival but I like the idea of him being a bit chill about so he can offer at least some reassurances. As a side note, Castiel can alter memories on request. He doesn't like doing but he will for a compelling reason.
Deucalion I'd like to bring in fresh. A chance to write out his initial reaction is hard to resist and he won't be any more helpful if he had been there a while anyway :)
He has no immediate plans for dropping any bodies.