Now you are going down the rabbit hole I went down a few year ago.   
 
Don't really know why raindrops are formed the way they are (educated guess is downward movement causes the shape due to air resistance)  but I do know by observation that a collection of raindrops form a level surface once it collects on land.  A body of water always seeks level, always. 
I know the sun and moon are light sources based on what I see.
I can't answer the first two questions in detail without getting into religion which is my personal belief system as opposed to me believing (without testing) what I read from mainstream science community.