"Any statesman of the day would consider Florida a minor player to negotiate with, due to its smaller population."
Unless you consider the fact that that would give the Army a 2 pronged approach into the Confederacy if and when his negotiations succeeded.
The South was already stretched thin to defend what they had across one border. Open another and you've got the makings of a quick disaster.
Especially being outnumbered what? 3 to 1?
Good point, but were Union military planners on the ball that much in March 1861. I'm not that familiar with Cameron, but I know McDowell wasn't forward thinking, as he showed at 1st Manassas.
The story mentions letters, not a single letter. It's likely that Lincoln wrote similar letters to all the southern governors, and this one is only one of them.