It seems like I have settled into a pattern of 12 guns per division, until I pick up a 4th division. In the first three I use Napoleons and 10lb ordnance. That keeps generally in line with what the Union artillery used. In the 4th division I add a heavy battery of either 24 lb howitzers or 20 lb Parrots. The 4th division usually doesn't come into play until the larger battles and the heavier guns have less mobility. I have considered Wiards or Whitworths to experiment on how well they do, but have not tried them out yet.