So Infantry and Motorized can go into an Infantry brigade.
I know Arty can go into an Arty Brigade but can AA and AT gun battalions be put in the arty brigade or are they only support companies?
there is no dedicated Arty Brigade, you can put ART,AA and AT into any other Brigade whatever there is iirc.
And ofc there are support ART,AA and AT. They have less guns and ofc less combat value but they won´t slow down the faster battalions.
Wrong.
There are 3 types of Brigades: Infantry, Mobile, and Armor.
An infantry Brigade can contain any infantry type: Infantry, Mountain, Naval (Marine), Airborne, and for some reason Art/AA/AT
A mobile Brigade can contain any mobile type: Motorized, Mechanized, Cavalry, and Motorized Rockets.
An armored Brigade can contain any armor type: Light, Medium, Heavy, Super Heavy, Modern/MBT, plus SPArt, SPAA, or TDs.
So:
1) You can have an artillery (only) Brigade.
2) You can mix and match within a Brigade as long as the type stays the same, so you can put all of your TDs, SPArt, and SPAA in one brigade (but not in a brigade with Motorized).
3) You can mix and match Brigades within a Division (to a max of 5 Brigades of up to 5 Regiments/Battalions)