Regarding case material for productizing, you could consider a combination of plywood and bent sheet metal, eg like a Moog. Also check out dato.mu for a few examples of kid proof synth enclosures.
That depends on how much effort your spend on finish work. Files and sandpaper works wonders, but that take time. Or you can fold the edges over so that the sharp edges are on the inside (cars do this). The plywood is likely to cover all those sharp edges - plywood is easier to shape than sheet metal so this is a common cheat that can look good if done right.