You speak of "inertia", but it bears repeating: Absent the contingency of war, Lincoln had no authority under the Constitution to address slavery in any form. True, he was no revolutionary, no John Brown.

What troubles me is critics typically attacking what he said without reference to what he actually did. E.g. first the Emancipation Proclamation, then mustering of sizable negro infantry, approving Special Order #15, forming the Freedman's Bureau, ensuring passage of the 13th amendment. Primary, though, was seeing the war through to its successful conclusion. I can't imagine any other possible leader who might have done this. Most abolitionists were pro-secession, & radical Republicans sought to put Confederate leaders on trial for treason, so it's to imagine Lee et al would have surrendered under those circumstances.

Lincoln's reply to Horace Greeley reflects that priority: without Union there's no point in having any position on slavery because it would out of their control.

Liberia was the principle colony for freed US blacks, but it's interesting you mention Sierra Leone. In the 1820s Paul Cuffee, a black ship's captain formed a society to relocate freed people to Sierra Leone. In spite of being funding by affluent blacks & white abolitionists it was never very popular. Later Martin Delany, the first black man admitted to Harvard Medical College & the first to achieve the rank of major in the Union Army also promoted colonization for freed slaves. Lincoln did advocate it for a time. The administration sent a group of about 300 to Ile à Vache near Haite. It was a disaster. Many succumbed to disease. The survivors returned. Lincoln had pretty abandoned the idea by war's end.

Anyway, the project of sending 3 to 4 million people anywhere was far beyond the capacity of any shipping available at the time.