Nice post and nice to have a short list of lessons kind of in one place.
I think a lot of people could benefit from more like this.
Even recently I've been thinking a lot about how it seems this is all FAR more complex than it really is. More drama than necessary. More heartache and pain for some.
Being/living poly (and this is something we've said many times in various ways) really is just a certain amount of good common sense about how you would want to live in a loving way in a loving world. Kindness. Consideration. Communication. Education. Not necessarily all in any particular order.
I suspect as we look at your list - or any other entries that follow - we'll discover that they all come down to such a short list of common elements. Learning to understand ourselves as well as others with an eye towards compassion and a common benefit.
Not really as difficult as it might seem from the outside once you reduce it to some fundamentals that aren't such a bad prescription for everyone (minus any labels). Maybe when you approach things from a perspective of "what's the best we can build that will benefit everyone" what seems complex gets considerably simpler ?