Could both "essere" and "stare" be used with feelings (eg happy, calm) and attitudes (eg silent)?
It seems to me that yes. On the one hand, "stare" is used in sentences in imperative mood, ordering/suggesting a change of feeling/attitude. On the other hand, "essere" is used in statements, describing a current/permanent feeling/attitude. Examples:
Stai calmo/zitto/felice! = Be calm/silent/happy! (requests a change of mood)
Sei calmo/zitto/felice = You are calm/silent/happy (current/permanent state)
Is that right?
I am especially not sure about "essere" always being used with statements with feelings/attitudes. https://langsandlit.tumblr.com/post/161368437468/essere-we-use-essere-to-express says that "essere" is used with permanent state and "stare" with current state in this case, but I do not know if that is standard Italian.