As a student of the Civil War and one who grew up in the South, I would add to your comments that the slavery issue was actually part of the larger states rights issue. The south wanted the right for the states to independently determine their stance on slavery, while the north wanted the federal govt. to mandate a stance to all the states (i.e.: abolition).
You are correct, that Lincoln waited to force the slavery issue. People were split on the issue of slavery, whether they lived in the south or not (especially in "swing states".) Lincoln was concerned that taking an abolitionist stance too soon, could drive borderline states (like Maryland) to the Confederacy. It was only after the Battle at Antietam (Sharpsburg, MD) that he felt confident enough to dust off the Emancipation Proclimation. His overriding goal was preservation of the union.
Antietam
Other Names: Sharpsburg
Location: Washington County
Campaign: Maryland Campaign (September 1862)
Date(s): September 16-18, 1862
Principal Commanders: Maj. Gen. George B. McClellan [US]; Gen. Robert E. Lee [CS]
Forces Engaged: Armies
Estimated Casualties: 23,100 total
Description: On September 16, Maj. Gen. George B. McClellan confronted Lee’s Army of Northern Virginia at Sharpsburg, Maryland. At dawn September 17, Hooker’s corps mounted a powerful assault on Lee’s left flank that began the single bloodiest day in American military history. Attacks and counterattacks swept across Miller’s cornfield and fighting swirled around the Dunker Church. Union assaults against the Sunken Road eventually pierced the Confederate center, but the Federal advantage was not followed up. Late in the day, Burnside’s corps finally got into action, crossing the stone bridge over Antietam Creek and rolling up the Confederate right. At a crucial moment, A.P. Hill’s division arrived from Harpers Ferry and counterattacked, driving back Burnside and saving the day. Although outnumbered two-to-one, Lee committed his entire force, while McClellan sent in less than three-quarters of his army, enabling Lee to fight the Federals to a standstill. During the night, both armies consolidated their lines. In spite of crippling casualties, Lee continued to skirmish with McClellan throughout the 18th, while removing his wounded south of the river. McClellan did not renew the assaults. After dark, Lee ordered the battered Army of Northern Virginia to withdraw across the Potomac into the Shenandoah Valley.
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