Expanding Brain

A simple answer to the second question is the first law of thermodynamics. Since somethingness could not have come from nothingness, the presence of somethingness precludes the possibility of nothingness. (The existence of somethingness can be proven by the act of asking "does something exist".)

A more semantic answer is that the concept of nothingness would exist within itself, and that duality would in fact be something. (This sort of answers question 4.)

So existence is eternal, extending infinitely in all directions, containing everything that could ever be, thus answering the 3rd question. (I don't have words to describe the existential terror I experienced upon puzzling out that existence has no option not to exist.)

The answer to the 1st question is implied in the answer to question 3, but a more direct (and existentially terrifying) answer is that your dad ejeculated into your mom's birth canal. 😮

The most likely answer is that you are a Boltzmann brain

True, though probability aside, every possibility reoccurs infinitely.

You exist because God made you and breathed the breath of life into you. There is something rather than nothing because God created the world. He created the world so that we could love and glorify him. And the other two questions I don’t really understand…

God is was and always will be.

Yep

Some use the dark energy analog.