First, I do not think you have put in adequate prominence, at starting, Heb. 10, distinguishing the Spirit's work which gives us the sense of our sins at conversion (and can only of past ones) and Christ's work when all were future, and the efficacy of which was not only up to the day of our conversion. Next, I believe 1 John 1:5-10 to be abstract—the message received from Christ come. Chapter 2:1, as you say, is clearly believers; but confession of sins is at the beginning and all along. Walking in light, fellowship, and cleansing, are the three elements of the christian state. Chapter 2:1, as you say, begins with the saints: it was for them he wrote what went before, but what he wrote was abstract truth, the message. But I think chapter 1:9 is present application: uprightness in confession brings forgiveness in relationship—not merely justification.