David,
I find some agreement in your understanding of the situation. I am not aware of the Florida part of it. It may or may not be so. I don't know. I have always been under the impression that Davis did indeed order Beauregard to do it. I like you don't know where the warship went other that withdrawing it was intended to defuse the situation some what. Anderson moved out to Sumpter because he felt that Moultrie was not tenable as I understand it.
I think that he (Beauregard) indeed might have thought that he was under attack. As I understand it, the ship that the Federal's sent to resupply was only carring basic suppies for the troops in the fort. It has been conjectured that there had been a plan to increase troop strength in the fort but it never came about.
In any case once Federal troops were fired upon, Lincoln did what he promised in his first inaugral speech.
Frank