First of all, Objectivism is not materialist at all (neither Idealist). Ayn Rand doesn't thought that the mind was reducable to matter. The reason she was atheistic, is because she was rationnal. Her experience in the Soviet Union has given her an idea of how men can be vicious, the damage of altruism, and the need for a real response to evil, because she tells herself how much the "whites" contributed as much to the evil as the "reds ".
Contrary to what many people think, altruism doesn't mean benevolence towards others. Altruism means self-sacrifice for others, this is the definition used by Ayn Rand, the definition of Auguste Comte who was the creator of the concept of altruism. Objectivism is not compatible with altruism, but fully compatible with benevolence towards others, as long as those actions benefit to you ; in others words, as long as you value them.
About environmental issues, I really advice you check out Alex Epstein. Actually there is no catastrophic climate change.
Anarcho-capitalism is incompatible with Objectivism for many reasons. Check out my Youtube playlist : Objectivist critics of anarcho-capitalism. (Maybe watch first the video: IDOAR #11: Damned to Repeat It, Pt. 2 - Anarchism)
I was socialist, leftist, close to anarcho-communism when I was younger. Shifting helped me a lot to solve psychological troubles. I was disturbed by many contradictions. Yes it made me happier in general. It's sane to stop blaming the world or society for all your problems.