I can use my son's 220 stick welder, just have to keep an eye out for the little girls when they come around.
For now any cutting would be with a sabre saw, sawsall, hacksaw, grinder and chisel.
On this 4" channel the top and bottom steps would be a straight cut. The center step would need a slot cut for the post to pass through. If I was still working I'd use a torch to cut it out.