that the higher the gravity the planet has, the larger and more radioactive its magnetosphere is. Jupiter's magnetosphere, for example, would be hazardous to space travelling humans.

Twice the diameter. So r is doubled. Works out to be a bit more than 4x Earth's gravity at the surface. Still not pleasant.

Magnetic field? Depends on rotation and whether the core's liquid. Since it's 11 billion year's old, that rather depends on the amount of radioactive isotopes present in the core.

Jupiter's got a strong magnetic field (which by itself probably wouldn't kill) because of the metallic hydrogen core and its fast rotation.

Since the air pressure applies equally to every part of your body, you don't experience any pressure difference, so no force due just to the atmosphere. If your body was slowly adapted to high pressure in a pressure chamber, or by slowly diving deeper in the ocean, you could live and function at that pressure pretty normally -- as some underwater habitat dwellers have done for weeks and months at a time.

To creatures from a planet with a thin atmosphere, our atmosphere would seem "crushing" -- it's a relative term.

sleeping in a hyperbaric chamber. Here I thought all these celebrities like Michael Jackson and Liz Taylor and Madonna were trying to prevent aging by "allegedly" using hyperbaric chambers, but they were really preparing for life on extraterrestrial planets.