My wish is to create rationalist communities which are emotionally healthy, capable of action, and successful in life. […] Similarly how the Sequences are not about "how to think rationally during a meetup", but how to think rationally in general.

Is your wish actually to create rationalist communities which are emotionally healthy, capable of action, and successful in life so that you can become these things?

That people often try to avoid an extreme by running into the opposite extreme […] and it will be necessary not only to navigate them properly, but also make them notice when someone else promotes an extreme form of behavior.

I think the problem here is that the underlying problem that caused these people to take on an extreme view in the first place is still there and so when they do change their view they just tend to adopt another similarly extreme view. For example you mentioned PUA before; I have noticed that there are some men who have a strong level of neediness and so become ‘nice guys’ in the worst sense. They then read some of the PUA stuff and instead of doing good things like: developing genuine confidence, self-respect, a healthy sense of boundaries etc. they take a shortcut. They just change their perspective on women. The neediness is still there, however, and so they adopt a view where they objectify women. They essentially become ‘assholes’. In both the ‘asshole’ and the ‘nice guy’ cases there is a sense in which these people are giving up or altering part of who they are. This is what I think these people would actually need to solve if they were going to make an improvement in their situation.

But people are less unique than they imagine. For example, read Games People Play -- this book describes about a dozen patterns of dysfunctional human interaction, and most people are shocked to find their own story described there.

That’s probably true, but I was trying to say that unlike with cognitive errors, which most people can relate to, most people would only be able to relate to a few of the games and would find the others to be largely irrelevant for them.

one of my big concerns is that I think that successful groups sooner or later attract psychopaths who will try to get into positions of power and exploit the whole thing for themselves. No idea how to prevent this

I would expect that any group like the one you propose would have a very flat hierarchy of power. In fact, if people become dependent on the group or find themselves seeming to need the group to improve then the group probably isn’t working too well. You reduce dependency by maximizing the free exchange of information and the ability for people to improve outside of the group.