Destruct1

That is an awful lot of soldiers. I used around 25000 and only defended the west part (mary height and telegraph road)

Exactly. The campign battles are to short for counterbattery fire; you need to help your infantry defend or attack with cannister shots. I think in a potential multiplayer battle long-range artillery is more important. The side which can snipe others from range can sit back and let the other attack.

Yup 24pnd Howitzer >> Napoleon > Ordnance >> 6pnd Field >> 12pnd Howitzer

Are 2 x 1000 man brigades worse in melee than one big 2000 man brigade?

While it sounds cool these ideas can backfire tremendously. Imagine that you need to commit 3 corps to 3 different battles up front and realize in the 3rd battle that you overcommited on the second battle and undercommited on the third. Now you need to replay all 3 battles. A complaint I heard fairly often was that the assignment of troops can only be done well if you know the battle. If you know Antitiam as the Confederates you put 11 good brigades and all your cav to the top Corp, a few brigades to the south Corp and the main bulk in the middle Corp. If you never played the battle you might be tempted to split your army in 3 equal parts. This is disastrous because it traps valueable troops in the souther part of the battlefield. Similar in gaines mill: You put almost all troops into the "frontal attack" Corps and barely use the flanking opportunity. If you think flanking sound cool you spend valuable time waiting for the useless Corps. Strategic campaign decision have the potential to be frustrating newbie traps.

You are wasting your time with small batteries. I always bring 12+ and most of the time 20+. Small batteries are better because the can turn faster and can be deployed better. But the real bottleneck is the amount of brigades allowed; it is not possible to deploy a bunch of small batteries.