How to assault an enemy unit?

[Indigo121]

Thank you all for the advice! More questions please:

1) How do I know which units have direct firing artillery? I've only seen one mortar inf have that.

2) I'm currently playing with art spotting turned off, so everyone can spot. Does that mean I'm getting poorer artillery results, or slower? I've read posts about spotting bonuses but didn't quite get what it implies here. How do I ensure best artillery results?
I assume mortars are faster than howitzers but do less damage, is that how it goes?

3) I notice air attackers follow enemy movements and don't necessarily hit the plotted position, and even often attack completely different enemies?

Thanks