Depends on the size of the details and how much time you want to spend. Basically, the smaller the tool, the smaller the details you can put in. For instance, if you have a panel line that is 1/16 wide, and you're using a 1/2" tool- the software is smart enough to know it can't fit in there and will ignore it. Now, you can get the rough shape with the 1/2 bit, then do another pass with a smaller bit to get the nice surfacing and details. That's how BishopX runs the armor and helmets. The trouble is you have to change the bit out manually for every pass. And each pass = more time. So depending on the details, it might be faster to do them by hand.
That's another one of those things I was talking about- deciding what do by machine or by hand is a skill in itself. You might think it's better to just let the machine do EVERYTHING, but some stuff will come out better and be faster to do by hand.
Some CNC's have automatic tool changers, the small one I am running the Magnum on does that.
As far as material, you want something that the machine will gradually eat away at- and has some kind of resolution. I'm not sure how the pink foam would work- you will probably have to adjust the speed of the machine to avoid melting it. Something cheap to try might be that green florists foam they sell at Michaels. or JoAnns. I've seen people sculpt that by hand for armor. Not the really soft stuff, the larger cell harder stuff. It's a dark green. The soft stuff is way too delicate. You drop it once or bump it and it's dented.
You'd have to seal it a hard coat- something like Bondo probably- but there's a trade off, in that now your material is cheap but you're trading that for time and work. And Bondo might melt it- I'm just thinking out loud. I'm not sure how it would work.
