Even if so (which is at best extremely dubious), that is not enough to envelop McClellan.
Yes it is, if Lee's operational art was up to it (it wasn't, but no-one knew that at the time).
The only army at risk of being destroyed is Lee's. McClellan's is pretty safe.
Lee is 6 miles from his supply base, on interior lines. McClellan's supply base is at the end of a long, exposed railroad. There is no danger of Lee being taken, but every danger McClellan will. Both Lee and McClellan recognised the situation and Lee tried to exploit it, McClellan tried to change it. McClellan's OODA loop was quicker and he won that race.
At Antietam? No. At Antietam, Harvey is a division commander, not a de facto "wing" commander.
As I say, Longstreet is a Division Commander, Jackson is a Division Commander; the officers commanding their Divisions on the day were the senior brigadiers who stepped up, as was the normal practice (although in Longstreet's case, like many CS divisions there was an intermediate level of command between Division and Brigade called a Demi-Division, it was the senior Demi-Division commander that stepped up).
In fact, there are initially 4 Wing Commanders on the field. Jackson with 2 divisions (Jackson's and Ewell's), Longstreet with 2 divisions (Longstreet's and Hood's), DH Hill with 2 divisions (DH Hill's and Walker's, both Dept of North Carolina) and McLaws with 2 divisions (McLaws' and Anderson's). There is some messing with structures certainly and they don't quite fight that way, but it appears to have been the way they were orbated under SO191. When the decision to collapse to 2 wings was undertaken, it was simply a case of putting DH Hill under Jackson, and McLaws under Longstreet (and certainly in Longstreet's Corps they continue to operate as 2 distinct "demi-corps", the move to 3 Corps again was a simple renumbering of Longstreet's Corps' Left Wing (McLaws and Anderson) as 3rd Corps, and transferring AP Hill's division in, making him senior Maj Gen and defacto Corps Commander until confirmed by Richmond as Lt Gen).
Show me a good artillery position on the Federal right...
No, all of them except possibly Bragg would have, because McClellan is facing <45,000 rebels with 75,000+ federals.
Hardly long odds.
McClellan didn't have that many. He had about 57,000 on the field, which includes his trains. Lee had about 40,000, but had already removed his trains back across the Potomac. Both had made considerable detachments to guard their rears (because both are professional soldiers).
Of his 57,000, about 10,000 (10,746 PFD) are "new levies", most of whom have never even loaded their muskets.
McClellan does have a slim manpower advantage on the 17th, but not a decisive one. Not enough to overcome the problem of having to attack on exterior lines against a well placed (although not entrenched) defensive line.
Since that counts Richmond's defenses and Holmes, that leaves Lee with 5:4 odds against him.
So much for double McClellan's numbers by this essay.
Yes, but the numbers reported are not the same numbers. The Union returns include detachments to the trains, hospital etc., while the Confederates generally omit these.
The actual combat strength of both armies is less than their PFD. For the Union the infantry brigades typically report about 50% of their PFD strength is with the colors (i.e. on average about 1,000 muskets per brigade), with the Confederates it's about 75% (i.e. about 1,750 muskets per brigade).
The ratio of formations (McClellan: Lee) is:
Infantry Brigades: 32:39
Cavalry Brigades: 2:3 (Stuart's "Brigade" is already operating as 3 demi-brigades)
Field Artillery Batteries: 57:73
Or in simpler ratios of man/gunpower
Infantry: 1:2
Cavalry: 2:3
Field Guns: 1:1