Napoleon's campaign was intended to split the Prussian and British Armies in Belgium, defeat them in detail, and consolidate those gains prior to Schwartzenberg and the Czar mobilizing in Germany to invade eastern France.
Both operations were undertaken with geographical and military objectives and with fairly detailed knowledge of both enemy strength, location, and probable movements.
Lee, at the start of the Gettysburg campaign lacked the first, and seemed unconcerned with the third. If you have a source that indicates memoranda, orders, etc. from Lee showing any of these things, I'd be honored if you'd share it/ them.
Lee's announced intention was to give the northern part of Virginia, especially the Shenandoah, a respite from combat and troops ‘living off the land’. The flip side of that intent was to ‘requisition’ whatever the Army of Northern Virginia could find.
When the meeting engagement at Gettysburg started, Lee had one Corps up near Carlisle, [Ewell], one Corps at the north end of the Blue Ridge mountains [A.P. Hill], and one Corps still coming up from Taneytown [Longstreet]. He had no idea where most of his Cavalry Corps was [Stuart] [although in fairness, Stuart left Lee with two brigades of cavalry he didn't much use], nor the Army of the Potomac. That's one hell of a campaign.
As to your second point, two Corps of Lee's Army, combined with Bragg's Army would have constituted the ‘largest military force’ the Confederacy could have mustered.
There is absolutely NO evidence that Lee's Gettysburg operation was intended as a ‘war winning knockout blow to [the South's] enem[y]’. Until the Iron Brigade was identified on the field, Lee didn't even know who he was fighting. And an argument he did militates strongly against the claim of tactical genius [based on that one battle], since Lee let the hostilities start when over two thirds of his Army was dispersed over an arc of considerable distance [Longstreet's last unit, Pickett's Division didn't close up until the night of day two - which was after Stuart showed up].
Gettysburg was not ‘an act of desperation’. It was an act of hubris. Lee could have pulled out at any time the first two days. He could have chosen to maneuver between the Army of the Potomac and Washington, D.C, and let the Union troops come to him. He didn't. He chose to engage in a series of dispersed frontal attacks against a superior enemy operating on interior lines some four miles shorter than his own. While Lee may have been a tactical and/ or operational genius [see Second Manassas, Fredericksburg, and Chancellorsville], he wasn't at Gettysburg.
And strategically, the South lost all future possibility of victory at Vicksburg, Atlanta and the March to the Sea. Lee didn't forfeit what chance he had until the Wilderness, when his penchant for offensive action [except at Frericksburg, and possibly second Manassas he always lost a higher percentage of his army than his Union opponent], finally ran up against the South's inability to furnish any more troops.
By the time Lee surrendered at Appomattox, the war had been effectively [not formally] over for months. Sherman had laid waste to Georgia and South Carolina, and was marching on Lee's rear through North Carolina [Lee's Army was deserting in droves]. Wilson was riding though Alabama on the biggest cavalry campaign of the Civil War. And AFTER Lee through it in Johnston surrendered the Army of Tennessee and the Trans-Missippi Department held out even longer.
I'll confirm a couple of points first.
On June 28, 1863, Lee's three corps commanders were Ewell, Hill and Longstreet.
Ewell, as you said, was north of Gettysburg, near Carlisle and York.
Hill was on the road which is today US 30, just west of South Mountain about 20 miles west of Gettysburg.
Longstreet was in Carlisle, with Lee, about five miles behind Hill.
First contact was about 7:30 AM, July 1, (DAY 1) between lead units of Hill's forces and Union cavalry, about 3 miles west of Gettysburg.
At 9:30 AM, Hill's first major assault, now two miles west of Gettysburg.
Ewell arrived from the north a bit later, his first units assaults beginning around 1:30 PM (still DAY 1).
Longstreet's units began arriving the next morning, July 2, (DAY 2) but his attacks did not begin until after 4:00 PM.
Longstreet's problem was not so much distance, as the fact that the only road passes through a narrow gap in South Mountain, through which both Hill's & Longstreet's corps must pass.
I have driven that road (US 30), and tried to imagine 50,000 troops with artillery and supply wagons filing through it.
Even on today's road, it would take time.
Why did Lee march north in June 1863?
Bowden and Ward argue at length that this was the South's "Last Chance for Victory," and they define "victory" as another major defeat of Union forces which would force the North to accept a political compromise.
And we must first remember that before Gettysburg was Chancellorsville, in early May 1863 -- in which Lee handily defeated a Union force over twice his size (130,000 versus Lee's 60,000 on the battlefield).
So both Lee and his troops thought they were on a roll, and could win any battle they fought.
A short explanation comes from Lee's after action report:
"Upon the retreat of the Federal Army commanded by Major General Hooker from Chancellorsville, it reoccupied the ground north of the Rappahannock opposite Fredericksburg, where it could not be attacked except at a disadvantage. It was determined to draw it from this position, and if practicable to transfer the scene of hostilities beyond the Potomac..."
So Lee was trying to force the Union Army onto ground that better suited Lee.
As to why Lee lost the Battle of Gettysburg, B&W argue Lee could well have won it, if the battle had been fought as Lee intended.
They provide a long list of failures, nearly all of which were ultimately Lee's responsibility.
But the fact remains that each of Lee's corps commanders in turn, plus Stuart of course, let Lee down at critical points in the battle.
Why they did so has been a matter on endless debate, these now nearly 145 years.
I'll give the final words to Lee. June 8, 1863, in a letter to Secretary of War Seddon:
"As far as I can judge, there is nothing to be gained by this army remaining quietly on the defensive, which it must do unless it can be re-enforced. I am aware that there is difficulty and hazard in taking the aggressive with so large an army in its front, intrenched behind a river, where it cannot be advantageously attacked.
"Unless it can be drawn out in a position to be assailed, it will take its own time to prepare and strengthen itself to renew its advance upon Richmond, and force this army back within the intrenchments of that city.
"This may be the result in any event; still, I think it is worth a trial to prevent such a catastrophe.
"Still, if the Department thinks it better to remain on the defensive, and guard as far as possible all the avenues of approacfh, and await the time of the enemy, I am ready to adopt this course. You have, therefore, only to inform me...."