The gravitational force equation actually takes into account the mass of both objects and their distance. The only reason we can throw out a gravitational constant of 9.81m/s^2 for most objects on Earth is because the mass of the Earth is so large that the mass and/or distance of the other object would have to be equally large in order to make any significant change in that value. Technically though, a bowling ball at sea level falls slightly faster than a bowling ball at the top of Everest, as does a bowling ball and feather from the same height. The reason is more accurately that they are experiencing slightly higher or lower gravitational forces, which cause them to accelerate (in conjunction with all the other forces acting on them).

In the same way that earth has gravity that attracts objects, the objects have gravity that attracts earth. See also Newton's third law, also known as "For every action, there is an equal and opposite reaction." - for the earth to attract something, the earth also has to be attracted with the same force. It's just that the earth has a lot more mass, so the force barely accelerates it.

Yes. And that force is proportional to acceleration so it accelerates earth

You got it.

No, because the earth is accelerating towards the bowling ball and the feather is next to the bowling ball, the force vector is (ever so slightly) greater towards the bowling ball than the feather, thus the bowling ball drops faster

That’s only be true if the feather was in the same position as the ball. Otherwise, the earth is moving ever so slightly more towards the ball.