I have ordered several naturally small-size fruit trees on medium vigor rootstock to espalier along my back fence. I was originally going to plant these in the ground, but long story short, I need to put them in containers now. What size container should I use? If all my dreams came true, these trees would grow relatively fast to their full size (which is small,) and would not need to be repotted since this would be a real pain given the communal trellis I have planned. Do the containers need to be extra huge and if so how huge?

Also, should I be concerned about toxicity of tree containers? For instance, if I get cheap pottery containers, could lead from the pottery into the fruit?