Have reinstalled and been playing Crown of Glory Emperor's Edition here recently so my ears perked up when you mentioned Napoleonic wars

Being only superficially familiar with 18th and 19th century military organization, I'm curious what "staff" would comprise? Would this be non-commissioned officers? Junior officers? Would these guys be on horseback or walking? Would be they be accompanying Lee or distributed throughout the army?
The one thing that sticks out to me as having been a rather major blunder on Lee's part: failure to direct his subordinates to retain sufficient proximity to one another to be self-supporting throughout the campaign. Disadvantages in intelligence, lack of staff, and defensive terrain aside, it seems to me that Lee's army was far too strung out, which made proper coordination and concentration of force at a favorable point an unlikely eventuality given they were marching in hostile territory deep behind enemy lines.
I mean its bad enough that he gives Stuart vague and open-ended orders that contribute to an entire cavalry corp being absent for most of the battle and completely useless to support the army. On top of that Ewell's corp is spread out all across the north, Hill's corp is spread out, and Longstreet's corp is so far behind it didn't arrive until Day 2?
Would it have been that difficult to advance north with the cavalry held in close reserve and small screening parties of troopers advancing a mile or two in advance of the army, as well as with each corp properly arrayed to deploy intact in a timely manner? Hell, Ewell's and Hill's Corp were so strung out, I think I read that Lee himself didn't even arrive until very late on Day 1?
Just seems strangely unprofessional and sloppy for a man who was clearly such a gifted General.
Even if the operational organization of the ANV as it advanced had been 'proper' the other factors described may well have still led to defeat. But deploying into an enemy occupied battlefield in dribs and drabs and engaging piecemeal seems completely antithetical to the goal of _destroying_ the enemy army.
I wouldn't have guessed that Robert E. Lee would have been vulnerable to 'over-confidence' as a result of the CSA's relative success with their audacious efforts up to that point. I suppose it is safe to say that the CSA was "winning" up to that point, but that is a rather squishy concept I think. Despite the various stellar victories the CSA had achieved, they had also had a few very close calls if not pyrrhic victories which were far too costly in blood and treasure. Not to mention that, as the video Calvin809 posted points out: Lee was keenly aware that what he needed to do was not simply to win battles but to destroy enemy ARMIES. He was a smart man so he must have been aware that many of the CSA's victories had been as much attributable to poor Union leadership as to CSA esprit du corps.
So on the one hand, I cannot imagine Lee getting sloppy in the operational execution of his campaign as a result of over-confidence. But on the other, his operational execution of the advance does seem to have been completely lacking and set him up for failure at GB.