He knew that if he did nothing then the forces in Fort Sumter would be forced to turn over the facility to the Davis regime. He knew it was a tense situation, which is why he made his intentions clear to Governor Pickens in a letter outlining the peaceful intentions. A letter delivered well before the projected arrival date of the supply ships. Lincoln did what he could to ensure that the status quo would be remain in place. It was Davis who forced the issue.
You seem to put great emphasis on Lincoln's words as if his words alone are all the proof any student of history would need to understand that Lincoln was just trying to keep the peace. Bull!
And you seem to think that it was Lincoln goading the Davis regime into firing that was the sole reason for the war. Likewise bull. Davis needed a war worse than you claim Lincoln did. He knew that his rump 7 state confederacy had neither the free population or the industrial base to thrive. It was doomed to dependency on someone, either the U.S. or Europe. Davis knew that if the south was to succeed then it would need the other 8 slave states. With those states the confederacy would have a larger population and some semblance of an industrial base. Davis knew that only a war would bring those states into his fold, and gambled that a war could be won. He gambled and he failed. It could be argued that any chance of an independent south died at Sumter, and it was a victim of a suicide orchestrated by Jefferson Davis.
You state that Lincoln's letter to Pickens justified his decision to send the fleet to Sumter. But... you dismiss and excuse the political reality of why he did it.
Sure, he may not have wanted the South to have Sumter... but why? Why did he dig his heels in over that one fort. If peace was his true end-game, then why not just give them the fort. It's not like the fort could sail up the Atlantic and fire on Boston.
No, he wanted that fort because he knew and understood that war was coming.
Furthermore you then justify Lincoln's action by railing against Davis... It's a red flag and a diversion. I hold Davis as equally culpable as Lincoln. I don't try to excuse what Davis did... What would be the point? Davis was just as politically motivated as Lincoln was.
So... the gist of your argument seems to be that Lincoln's motives were as pure as the driven snow (after all, he sent a letter) and that it is evil Jefferson Davis that deserves all the blame for the bloodshed of the next four years.
Sigh...
Bruce Catton made the point, and "The South Versus the South" by Dr. Freehling also makes the point that once the border states were secured to the Union, the south was absolutely doomed.
The war was decided in the first year.
Walt