I’ll just respond to your comment about the third proposition for starters. Here “God is…” obviously is not a claim about existence, but about the notion of God. A good example of this among atheists is Richard Dawkins who says that his main reason for not believing in God is that a complex being like God, is not going to be explanatory. You can watch the first five minutes of his interview with Piers Morgan if you want to hear what he says.