On strapping, use the nylon webbing for strength and the elastic where you want some give.
When I first attached my bicep pieces to the shoulder bells, I used nylon. They would pop off just about everytime I suited up because there was no play there when I moved my arms. I switched to elastic and they have held ever since.
I only used nylon for the shoulder connectors, connecting the bells to the shoulder connectors, the sides of the ab plate and the thighs.