You could put a wrist thong here too. An intelligent sheath. Look for one with a release operable by one finger of the hand that's grabbing the knife. It should let the knife withdraw smoothly. The sheath should also have mounting options beyond the usual pair of leg straps, like a belt loop and bolt holes.
Higher numbers mean less corrosion resistance, but more ability to hold a sharp edge during use.
A harder stainless steel knife would have lost its edge to corrosion long before. The edge will be sharp but rough, as if it had tiny serrations. It will slice through any rope much faster than a stone-sharpened edge. As with a stone, try to keep the file at a constant angle and file both sides equally. The easy way to sharpen it is to take a stone to the other edge and sharpen it as if it were a plain edge.