Going by mass, the solar system can be said to be inhabited by the Sun, Jupiter, and various minor bodies.
Saturn has a density low enough that it would float in water, provided one could procure a large enough bucket.
Mercury is the densest planet. It is theorized the lighter layers were stripped away by the solar wind, leaving the iron core behind.
All elements are made by stars. Everything lighter than iron is made during fusion, and the rest are made during the immense pressures inside supernovae.
A black hole can grow to a theoretically infinite mass. In fact, it is at least possible in principle for all the mass of the universe to be contained by one black hole, but that sounds inconvenient.
Jupiter's moon Europa has more water than Earth.
Saturn's moon Titan has more hydrocarbons than Earth.
Planets shift the angular momentum of a star outwards, which prevents the star from breaking under the force of its own rotation. Any star which isn't a binary most likely has planets.
The Venusian atmosphere weighs 94 times that or Earth's, which allows it to hold more heat. This accounts for Venus' high temperature.
Gas giants are really fluid giants, as the immense pressures in the lower layers force the gasses to become liquids. Jupiter likely has an ocean of liquid hydrogen somewhere inside.
Saturn's rings were likely formed by the collision of two moons eons ago, which provided the basic building material.
In some deep valleys, the temperature and pressure on Mars can become high enough for liquid water to exist on the surface.
The moon was split away after the layers of the Earth differentiated, which means it is composed largely of light elements.
Jupiter's moon Io is the most active body in the solar system, volcanically speaking.
Venus is the only planet that rotates prograde, meaning that the sun rises in the west. Why it should do such a thing is still a mystery.