ACM panels are great for non warping supports for anything, but they really shine with with water based stuff. They are easy to cut in straight lines with nothing more than a craft knife and a metal straight edge, but not so easy to cut into curved or irregular shapes, unless you have a mini router or water jet cutter. 3mm is the thickness I use the most. 2mm is nice for small and light stuff but bends quite easily, 4mm is what I pick for larger than 24" panels.
If you lightly sand the surface without breaking through the white polyester coating, then prime with XIM UMA bonder / primer, any type of paint or glue will adhere well.
This post gives quite a bit of information on various brands of ACM panels.