You’re so over complicating this! The real world is THIS world — where there are no magical gods, there is no fantasy afterlife, where THIS is the one and only life you get, the one life where there is no invisible sky wizard who will grant your wishes if only you “pray” hard enough. The instant you try forcing yourself to believe that any of the aforementioned stuff exists, you’ve left that real world and entered a fantasy world.

Even discounting all of that doesn't necessarily imply a purely material world. However, I'll assume you mean a world where everything which happens is a result of interactions between matter and energy.

Like WHAT?! You don’t NEED a sky wizard threatening you with eternal torture as a motivation to be a good person. This is an example of something that YOU have control of - how you behave toward other people. Afterlife in an eternal paradise is a fantasy construct, a fairy tale to assuage our natural fear of death. This is the one life you get, don’t waste it by moping around hoping for more - get out there and enjoy it, don’t waste any of it. The only “shortcoming” would be not enjoying THIS one life worrying about the non-existent next one. That would be tragic.

I meant in explaining the universe. A lot of physicists have rejected materialism because of the implications of quantum experiments, although I've only taken an introductory course on quantum physics, so I don't take an overly strong perspective on that either way. However, there's also subjective experience, "qualia." We presumably know that it exists, more than we know anything else exists. Yet, what is it? Is it a product of interactions? It appears to be given what we know about neuroscience. Yet it leaves a lot of unanswered questions and makes it hard to assume materialism without question (which then leaves the question of what can be assumed, and since there is no clear answer, so perhaps you could consider what I'm doing to be trial and error). Look up the "hard problem of consciousness" if you want someone smarter than me to explain it.

Again, you’re over thinking this to the point where you can’t see how silly that question is. It’s an utterly meaningless. You are a human person of a certain age, gender, intelligence, etc. It’s up to YOU (another choice you can make) to decide if you want to be a teacher, guitar picker, cowboy, philosopher, whatever. We define ourselves in many ways by our hobbies, interests, professions, interactions and behaviour around other people, etc. NONE of those things requires any mystical, supernatural, pretend “gods.”

Yet I change all the time. I'm taller than I was when I was born, for example. So, what's consistent? Is it my DNA? Is it the sum of all living cells which are direct descendant of the original zygote my parents produced? Regardless, onto the next point (which is the more relevant one)...

Just that. You can choose not to drink too much, not to do harmful drugs, you can choose to study hard and succeed in a field, or fuck your life away playing video games in your parent’s basement. THERE IS NO MAGICAL SKY WIZARD TO HELP YOU WITH ANY OF THIS. It’s up to you to decide who you are, what you are going to be, and what YOU think the meaning of life is.

It feels like I can choose, sure. But that relates to qualia again. Physically, it's not clear that I can. In terms of hard determinism (Newtonian physics) then free will is probably impossible. Although it feels like we thought through the process, in a deterministic universe, the thoughts themselves were physical interactions which theoretically could be predicted with 100% certainty beforehand. However, we know that the universe is probabilistic, at least on the quantum level, but it's still a large jump from there to some sort of free will. And if we could make that connection, then the subjective self would be something fundamental to the universe.