If these are loose strip liners (like wall paper), they will be seal welded along the perimeter. I would consider straight E309L weld rod for seal welding the liner to the carbon steel substrate. As far as liner width and length, it is really up to the contractor to decide because warpage of the loose liners from exposure to post weld heat treatment of the vessel could be a problem ( stainless steel expands at a greater rate than carbon steel). I don’t believe there should be any gaps between the edges of the liners, the edges should be butted together for seal welding.
What are your service conditions for the pressure vessel?
One option to using strip liners is to evaluate strip cladding. The strip is the welding electrode and is deposited by SAW or ESAW processes for high deposition rates. The strip cladding will be fused to the carbon steel substrate, and will not warp from post weld heat treatment of the vessel. Something to give serious consideration.