I did a cursory analysis as a Union player last night and it is indeed possible to muster nine mostly militia Divisions for the supply depot cities I mentioned, two mountain Divisions for Fayette PA and Fulton MD, and still have a three Division Army stack for HF, D.C. and a Reserve (with absolutely nothing sent to Alexandria). The Reserve stack can even have a cavalry Division and three cohesion boosting brigades, one for each infantry Division, which come in handy for a mobile reserve.The Divisions themselves are subject to leader activation, but the troops should be in place by October '61. Then I would humbly suggest that a Union player finish building a riverine fleet so that New Year's Day 1862 can be celebrated in a Union Fortress that would impress even Vauban. No city with defenses built by this Frenchman was ever taken. (Of course, you all already knew this.)
As to the battle-worthiness of the militia Divisions, I can only report that in the completely different battle mechanic of AACW (which font is for sarcasm?) I was able to slaughter one fifth of a 50k CSA force that came to Louisville "licking their chops" and left licking their wounds. The depots that I don't need would be destoyed by the cavalry elements out west as they moved east to that Reserve army. Anything that can be organized, can be done.
The nine depot cities generate enough GS for over a dozen Divisions, so they don't need to be plugged into anything else, although Pittsburgh would be getting supplies from the east. The defenders would be entrenched inside the cities for extra defense. I know that slaps another bit of CW in the face (Have I omitted any CW?), but if you read the frontage and seige parts of the Wiki, you'll see that it works. You must have a supply wagon present so that the defenders don't surrender and then the offenders get to slaughter themselves. If a Confederate flag flying over Chicago bothers you, I might point out that NY state contributes more to the war effort than all of the midwest combined. So defend what counts. Any Confederate leader who wastes armies attacking the midwest gets a Union medal when I take Richmond.
As I posted elsewhere, an educated man can only spell experience. Unless you spent 21 years being educated by the U.S. Army (my favorite real army).