Good day Imp
Did a little looking around and here's how I figure it. AAA assets were assigned at Division level as an AAA Bn with 12 light AA guns. What these 12 guns were really depended on the unit and dates etc. Looking though various Orbats and TO&E's KG's and Bn's were assigned AAA from Div and for a KG your size 4 AAA pieces would not be out of line.
As for types, that really from what I could see depended on availability. I saw units with no AAA, a mixture of towed pieces and SPAA, all the way to units with 251/17 20mm with every Pz Gren Zug (this being an exception although desired). The most I saw besides the later was units KG's with 6 pieces usually at least 2 or more being towed.
Sorry there does not seem to be a set answer but I think this sure give you some guidelines, most certainly for game purposes. BTW I also saw units with just about every AAA piece being different so mixing it up especially as time marches on doesn't seem out of line either. Early war units I would recruit your AAA sections with all the same kit. The odds and sods approach was seen in the later years.
I hope this helps.
Bob out
