Starting with a POD after the election of Lincoln, what sort of alternate ACW beginnings can we have? I have a hard time getting beyond the Ft. Sumter incident.
Where else could the first shots be fired? In Kentucky? Missouri? Where would the Union attack first?
As noted, Lincoln wanted to avoid firing the first shot; Davis felt the CSA had to Do Something to assert its sovereignty. Sumter was a flashpoint because it was a Federal post in "CSA territory". However, there were two others, both in Florida: Fort Pickens, at Pensacola Bay, and Fort Jefferson, in the Dry Tortugas near Key West.
Fort Jefferson was practically untouchable by the CSA, and so far offshore as to be irrelevant.
Fort Pickens lay right on the shoreline (on the spit of land between the bay and the ocean), not under mainland guns and thus not besiegeable. Between the inauguration and the bombardment of Sumter, Pickens was almost as big a question.
Seward wanted to give up Sumter: in part because it was indefensible, and in part because holding Pickens would make the same point. Seward in fact made a secret promise to Southern representatives that Sumter would be evacuated. He thought that it would help defuse the crisis and avert secession by the Upper South. Lincoln had to remind him who was President.
If Seward had his way... Or another possibility.
The US force at Charleston was stationed in Fort Moultrie, on the mainland and defenseless. There were only some construction workers in Sumter, until Major Anderson moved his men from Moultrie to Sumter. The South Carolina militia might have anticipated this action - they could easily have stopped it, or moved into Sumter first. In which case, yes, Pickens could be the site of first combat.
Another possibility is Virginia. The state convention refused to vote secession, and the hardline secessionists became frustrated. Some of them had plans to form unofficial militia units, seize the Norfolk Navy Yard and Harpers Ferry Arsenal, and impose de facto secession on Virginia.
IIRC, the attacks were scheduled for late April, and were pre-empted by the Sumter crisis and Virginia's official secession. There were enough Marines and armed sailors at Norfolk to make a fight. Quite possibly the action would backfire. Virginia was legally a state of the Union: free-lance paramilitaries killing U.S. Marines and sailors in the name of Virginia would be a colossal embarrassment. Most Virginians still opposed secession, and an outlaw attempt to stampede the state would be repudiated.