Just an idea for shoes, two blocks of wood (in the shape of the shoe) on either side of the leg bolted together through the metal. Glue some strips of rubber on the bottom of them for grip or just cut the ends of the wooden blocks to be textured. What you do with the bottom of the feet really depends on what the robot will be walking on. Really smooth (like a wooden floor), use the rubber. Reasonably rough (like a playground), go for wood.

Looking really good.