3. How did the planets form?

Solid planets (like Earth) are made from gas and dust particles colliding and sticking together as they orbit a star. The more mass that is sticking together the more gravity there is. The gravity originates from the center of a planet, so gravity pulls down from every direction, creating a sphere.

It’s the same for Gas Planets as well, except there’s only gas and relatively no mass sticking together.

The sun's parallax would be 180 degrees, greater than which you can't get.  so a. would be your anwser