You need to describe the organization of such a society: how do things get done.

Why? How should I be able to? No one in feudal times could have predicted how things would be done in capitalism. Why should I be able to accurately predict how a free society would look like?

Who decides what gets done and how is it decided.

In my (limited) model? Federated councils. So the people have a say in decisions proportional to how much they are affected by them.

How do you stop those humans who are smarter, and more charismatic from rallying a following and imposing their will?

How will these “smart people” be able to achieve such a following? Immediate hunter-gatherers have strategies against this kind of accumulation of power. For example by ridiculing people who are too full of themselves. Can’t find the youtube video that explains this concept, right now. It was one in this series, though.

Also: you do realize that liberal democracy has this exact problem of demagogues?

The natural state of humanity is hierarchical

Now where did you get that idea? Any sources for that? Also: naturalistic fallacy.

I am simply making the descriptive claim that without guardrails hierarchy will form.

Maybe. Anarchists are quite in favour of these guardrails, though.

I think you overemphasize competition in mankind. One foundational text of anarchism is “mutual aid” by Peter Kropotkin, which adds on to Darwin’s theory by stating (and observing) that cooperation within one species is a vital factor in evolution.

Edit: Found the video I meant