I guess you and I have different views of how the military chain of command works. I don’t see a lieutenant deliberately starting a war without cover from above.
He didn’t start a war. Had Porter carried orders from the President to enter Pensacola Bay and provoke the Confederates into firing on his ship, he would have done so. If that meant having to ram the tug the Meigs on board to accomplish those orders, Porter would have done so. Porter did not do that. He stopped for the tug and Meigs showed him the order from Col. Brown to not enter Pensacola Bay. Had Porter been given a “secret order” by the President, Porter would have shown Meigs that order. Then told Meigs to get off his ship and allow him to carry out the orders of the President of the United States.
The fact that Porter did not enter Pensacola Harbor after being shown Col. Brown’s order, indicates to me that Porter was not in possession of any orders from the President other that those we already know about.
The reason for the British flag. The Confederates would not have fired on Powhatan if they thought she was British.
Clearly Porter was allowed some discretion, as was Ward Lamon in his arrest warrant for Judge Taney. And Porter did subsequently fire at Confederate ships while in Pensacola bay, and again with no knowledge on the events in Charleston.
Porter hid the ship to keep the Charleston mission from realizing it wasn't ever going to show up, and therefore they weren't ever going to try a foolhardy assault on the Confederates. Also to keep the Confederates from learning that it was never going to show up, and therefore those ships were never going to attack, and therefore there would be no actual need to bombard Sumter before the war fleet arrived to engage them.