Connecting buck converter to 10mF 40v filter capacitor
Q1: Your cap is seperated from main line, so voltages below 48V are no problem to touch. The resistance of your body is too high to let the current flow.
Don't know, what the buck-converter does. If any charge would increase voltage of your whole circiut relative to earth over 48V, then, to be a littly bit more safe, you could connect your secondary GND to Earth.