Both to the first question and why is there something instead of nothing, my answer is they are bad questions. The first is somewhat nonsensical. But why is there something instead of nothing is making assumptions that you have no reason to make.
"Why is there something instead of nothing?" Now when you ask this you have a very particular definition of nothing that I not only know that you aren't sure is right, I believe is probably wrong. We have this idea that nothing is empty space or something like that. Space (or in reality spacetime) is something. It exists. And things can pop out of it, but it's not nothing so that doesn't really matter (and that's an answer I've heard many scientific atheists give; they say quantum fluctuations account from something coming from nothing, but quantum fluctuations are not something coming from nothing, but rather they are something coming from something else). Energy seems to not be able to be created or destroyed (I actually believe that is probably wrong but I am not sure); everything seems to be rearrangements of something else and we don't know what we are actually arranging or maybe we do (for example energy or force may be fundamental, but they could not be as well). All we can see is something, and something has a bunch of rules that we perceive like causality and identity. When you ask "why is there something instead of nothing"" and say "nothing comes from nothing" you are making assumptions about the nature of nothing namely that it has some sort of causality and we can't perceive causality without time; causality may very well be dependent on time, so the fact that there is something doesn't seem so odd to me. Uncaused things may just begin existing from nothing because there is nothing stopping them. They don't necessarily need a reason unless nothing has a bunch of properties. I don't know for certain than nothing doesn't have properties, but to me it seems like it shouldn't.
Alright "why are we here"? Why is such a bad word. Aristotle talks about the four causes. People argue how they relate to our own view of causality and I have a particular view on what he meant, but that is not important. The cause you are asking for is what he called the "Final Cause". If it rained, Aristotle would say that it rained, so crops could grow. When people say "everything happens for a reason," they almost always mean that there is a Final Cause for everything, which I firmly disagree. I don't think the "Final Cause" exists outside of human interference. My metaphysical beliefs get admittedly shaky, because as a naturalist I believe we are natural, meaning everything we do is natural, so postiting a new type of cause seems as if I'm leaving naturalism, but it's only from our perspective, as it would be totally possible to view everything we do without a final cause, but our reason prefers shortcuts which the human final cause is. I don't believe it rains for crops to grow, as I believe that crops evolved to grow in the rain. I think whenever you believe in the natural Final Cause, you are reversing causality. I could argue, that you have to believe in backwards causation to believe that everything happens for a reason, but that's pretty complicated, and I don't feel like writing another page.
But keep in mind, if you don't think about it, we all believe in backwards causation. Newcomb's paradox proves this I would say, but then again most of what Aristotle wrote, we all believe instinctually (like his physics; even MIT students when not given proper time to think about the path of objects will give Aristotle's account rather than Newton's).
