Hi.
While I don't disagree with you that angels exist, there are possibly alternative explanations to the things you are describing, in this article and elsewhere. I don't know if you think an angel [St. Michael] sent you this dream. But it is usually believed that dreams come from one's own Higher Self, which is undoubtedly part of a process of guidance from beyond.
You say that you couldn’t possibly chalk up your experience with Kylah to coincidence, and rightly so, by which which you mean random coincidence. There is also, however, the phenomenon of meaningful coincidence, otherwise known as synchronicity. How this occurs is a mystery, but it isn't necessary to attribute it to angels. I prefer the explanation that the whole universe is the interconnected thought of the Divine Mind. I've written about this recently, if you're interested.
On a separate topic, you are probably right, and very wise, not to question how God operates. But it's great that you are trying to understand it all. Your experiences have probably reconciled you to the possibility that it was your son's time to go, and that this may have been his karma, part of a bigger plan.
I would say that this whole sequence of events was organised around the archetype of St. Michael. That doesn't necessarily mean that St. Michael was involved himself. But he might have been. What do I know?
Good luck on your journey.