I have only 1 layer of cloth, but I add extra resin on top of my layer to increase strength and save cloth. Although I recommend 2 layers for key parts such as the chest assembly and maybe the boots...prettymuch any part that you know is going to take the most punishment.
Alternatively, I've heard recommendations for using fiberglass MAT on the inside of each part to dramatically increase strength and duribility. I'll most likely do that before its all over.
But to answer the question - 1 layer's fine, but 2 is better...if you have a fat budget like I don't.
-JF