I've done a lot of posting about what I use for an army, perhaps a .jpg is worth a kilobyte of text.
An Artillery Division of 20-lbers:
[ATTACH]33185[/ATTACH]
An Elite Infantry Division with upgraded militia:
[ATTACH]33186[/ATTACH]
An Army of these units:
[ATTACH]33187[/ATTACH]
The numbers:
[ATTACH]33188[/ATTACH]
This is a minimum setup for what I would do as a Union player to make a good army stack.