Re 6 well actually, when people say they've lost weight, they're talking about the magnitude of their weight as measured; this just so happens to be proportiona

Re 6 well actually, when people say they've lost weight, they're talking about the magnitude of their weight as measured; this just so happens to be proportional to mass since gravity + centrifugal force is relatively constant on Earth. As to 8, well actually when referring to objects one would by default use a reference frame where those objects are approximately at rest. E.g. a reasonable reference frame would be one where the aforementioned center of mass is at rest. So it's reasonable to say the Earth and Sun are 8 light minutes apart.