You contend that after Sumter, they quickly reinforced the decks to carry the weight of a cannon, and maybe this is true, but at this point it is not unreasonable to think the Thomas Freeborn had a cannon on it prior to the Sumter Mission.
You also overlook the fact that the Confederate intel said there would be more ships than this coming, The Brooklyn being one of them, but at the time the Confederates had no real way of knowing exactly what sort of force Lincoln was sending.
What they did know with certainty is that a number of armed warships were coming, and they meant business.
If your read Beauregard's account of the Sumter incident, it is clear he expected not only a larger naval force, but invasions by marines and infantry that never manifested.
Lincoln's goal was to create the illusion of a force attacking the Confederates to goad the Confederates into starting the war, while at the same time convince the people up in the North that it was a "peaceful mission" with no belligerent intent.
It's like the same sort of lying we see today, like in the Keystone pipeline farce. They are claiming "environmentalism", while their intent is to make sure Warren Buffet keeps making that $30.00 per barrel he gets shipping that oil through his railroad.
“You contend that after Sumter, they quickly reinforced the decks to carry the weight of a cannon, and maybe this is true, but at this point it is not unreasonable to think the Thomas Freeborn had a cannon on it prior to the Sumter Mission.”
Not only do you have to reinforce the deck to support a 7,000 pound gun, you have to reinforce the bulkheads to absorb the recoil and you have to add a few tons of ballast below the waterline to compensate for the increased weight on the main deck. In addition they would have to construct a magazine for the safe storage of gun powder. The work could be done in a Navy Yard in a week or so. After Sumter, a week in the navy yard then on to operations late in April or early in May.
“Lincoln’s goal was to create the illusion of a force attacking the Confederates to goad the Confederates into starting the war, while at the same time convince the people up in the North that it was a “peaceful mission” with no belligerent intent.”
If Lincoln’s goal was to create an illusion of a force attacking the Confederates, why did he send Pickens a telegram stating that force would be used only if the Confederates resisted the reprovision of the Fort, that no guns or men would be landed. Why did Welles tell Mercer in his orders that if the Confederates allowed the peaceful resupply of the for with provisions, the war ships were to return to their ports. Why did Cameron tell Fox that the objective was to resupply the fort with provisions, force to be used only if the resisted the resupply effort. Strange Confederate intelligence learned an armada with marines and infantry was on the way, but none of the confederate agents in the War or Navy Departments picked up on the orders issued to the officers carrying out the mission.
None of this would make a difference anyway. Davis was not going to allow Sumter to be resupplied by anyone. If a troop of Girl Scouts showed up in open canoes carrying provisions for Sumter he would have ordered Beauregard to reduce the fort before the Girl Scouts could paddle their canoes into Charleston Harbor.