am at the point where I need to decide on how to attach these limbs before I make the molds.
My interpretation of what you want to do is that you have made the arms and legs in clay and now want to attach them to the clay torso before you make a mold. (I assume the mold will be rubber.) If that is the case, I am wondering why the joints need to be strong. A simple metal or wood pin would do, or even just the stickiness of the clay. To make a rubber mold, the only strength the clay model needs is to be able to support its own weight without de-forming itself.
Am I missing something?