All of your questions have no good answer at this point in time. All of them are being researched by physicists, cosmologists, and theorists. We don't even know whether our universe is the only universe or whether what lies beyond the visible universe is just more space like the kind we can see. Our best theories of space and time (Einstein's General Relativity) and particles (quantum field theory) only tell us about what the universe was doing a small fraction of a second after the big bang. We have experimental evidence from particle accelerators that confirms this picture back to one second after the big bang. However, what happened earlier, including the bang itself, is a mystery.
Other currently unanswerable questions and some entirely speculative possible answers:
- Was there just one big bang? Or, are other parts of the universe that we can't see still inflating? That hypothesis is called Eternal Inflation.
- Why do we only move through time towards the future? Perhaps there's another half of the universe that has been expanding backwards in time since the big bang. In that case, the time before the big bang is that universe's future.
- What happens inside the event horizon of a black hole? Perhaps a black hole is a place in one universe where a piece of spacetime became so warped it twisted off and inflated into a whole other parallel universe.
One more note, not only is the universe expanding, its expansion is accelerating. Something is pushing everything apart from everything else. That something is what we call Dark Energy (cue spooky music). We call it dark energy for two reasons: (1) it doesn't give off light, and (2) we don't know what it is. For the moment, it looks like the universe's expansion will continue to accelerate into the future and, trillions upon trillions upon trillinos (... etc. ...) of years from now, the universe will be expanding so fast that stars and planets will be pulled apart, leaving an empty void.
This picture will probably change as we learn more about dark energy and the rest of the universe. There are still so many questions left to answer.