It exchanges gravitational potential energy for kinetic energy. It loses gravitational potential energy. All of the above are correct. Kepler's second law, which states that as a planet moves around its orbit it sweeps out equal areas in equal times, means that planets have circular orbits. As a planet moves around its orbit, it sweeps out equal areas in equal times.
More distant planets move at slower speeds.
A planet travels faster when it is nearer to the Sun and slower when it is farther from the Sun. The force of attraction between any two objects decreases with the square of the distance between their centers. The orbit of each planet about the Sun is an ellipse with the Sun at one focus. According to the universal law of gravitation, the force due to gravity is directly proportional to the square of the distance between objects. According to the universal law of gravitation, if you double the masses of both attracting objects, then the gravitational force between them will not change at all.