Schleiermacher's two open letters to Lücke On the Glaubenslehre make for a good introduction to reading The Christian Faith. Given that common portrayals of Schleiermacher are deeply colored by critics contemporary to him, through Barth, Lindbeck, and present writers, a chance to hear Schleiermacher's own defense of his work as he was in the midst of revising it for the second edition is an invaluable tutor for reading The Christian Faith itself. One can still disagree with Schleiermacher, but one is forced to face Schleiermacher rather than third-hand canned characterizations of him. Likewise, the advice is good that was given to us as we began our seminar on the Glaubenslehre this past fall... reading the Glaubenslehre from cover to cover is a good introduction for reading it through a second time. It is a highly systematic and overpowering dogmatics that does not sprawl and circle around its object like Barth's lectures; as if the ingenuity of Schleiermacher were not enough in itself, he has condensed his insight into a tight structure that is only opened up upon first reading... unpacking and deep interpretation require its revisiting.
I would add to these observations that the letters to Lücke and the original critics of Schleiermacher themselves deserve revisiting after a first run-through of the Glaubenslehre. The main purpose of giving Schleiermacher the first word of interpretation and apology for the Glaubenslehre is to create some space amidst other commentary on his theological project that has piled up. If one hasn't read through The Christian Faith, then the first thing to do is let Schleiermacher speak and assume that what he is claiming for himself will be adequately justified in time. And most likely it will be-- Schleiermacher does not leave much room for dispute about the coherence of the whole of his work. It is difficult to bring into question one aspect of his theology without tugging at the threads of its entirety.
But once one has given him the time to share his vision in its entirety and to work off of the assumption that this vision comes together (and it does), it's perfectly responsible to come back to Schleiermacher with a more critical eye. Just as we shouldn't read the Glaubenslehre merely on the basis of second-hand critique of Schleiermacher, we also shouldn't merely settle for Schleiermacher's own critique of his detractors. James Duke and Francis Fiorenza have done a commendable job putting together a thick set of contextual endnotes for the English translation of the Letters to Lücke. We can easily get at the concerns of Baur or Braniß or Bretschneider through the apparatus of the American editors.
Another resource that has proved really helpful for me (would that all collected works of great thinkers be charitable enough to put together a two-inch thick volume like this!) is KGA I.7,3 - the third volume appended to the 1821/22 Der christliche Glaube in Schleiermacher's works. This volume is divided into two sections: one of marginalia and notes of Schleiermacher's, and the other of over 400 pages of excerpts from over 40 thinkers that receive either explicit or implicit mention by Schleiermacher in the Glaubenslehre.
Some of the more prominent texts here are translated into English somewhere, but many of them aren't available except in the German or Latin provided by KGA. I've also found that while some important works are overlooked in these excerpts, they can often be found easily enough in Google Books or another digital repository... it's all old enough to be on there and downloadable for free.