What Did Zelensky Know and When Did He Know It

It has seemed to me to be important to understand the timing of events. This post has some of it, but I've some unanswered questions:

• before Trump made the decision to withhold the aid to the Ukraine, were there any discussions in the US government about the possibility of doing so?  If so, did word of that possibility make its way to Zelensky?
• when Trump made the decision, it appears it wasn't particularly quickly circulated within the US government?  True?  And there was no official rationale for the decision, or at least Trump offered two conflicting post hoc rationales?
• when did Zelensky receive word of Trump's decision, and what explanation was given?
• what did Trump understand to be happening after he made the decision?  Did he regard the decision as something for him to follow up, as in the phone conversation, or was he at all relying on the Pentagon and State Department to follow up (unlikely in my mind)?
• when Trump was talking with Zelensky, did Zelensky know of the decision?  Did he understand any rationale for it (better investigation of corruption, versus specifically investigating 2016 issues and/or the Bidens?
• when Trump was talking with Zelensky, did he think Zelensky knew of the decision and understand the rationale. or did Trump think it was his role to inform Zelensky of either or both.