>>24455783 (OP)
For ancient takes on Platonism, see the introductions/handbooks/essays by Albinus, Alcinous, Apuleius, and the Michael Haslam article "Plato, Sophron, and the Dramatic Dialogue" on an Oxyrhyncus fragment on the mouthpiece question. See also the George Boys-Stones translation of the Anonymous Commentary on Theaetetus.
For prosopography, see Debra Nails's The People of Plato, which contains a thorough accunt of every historical personage in the dialogues, and how they're attested to in archaeology and in other ancient writers.
For phenomenological readings, see Heidegger's lecture course on Plato's Sophist, and his essays/lectures on the Essence of Truth from the early 30s (on the Cave in the Republic and from Theaetetus), and Gadamer's collection of essays (plus book on the Philebus and his book on Plato and Aristotle on the Good).
For Tubingen esoteric readings, see Hans Joachim Krämer's "Plato and the Foundations of Metaphysics."
For two older traditional takes that take the dialogue form seriously, read Schleiemacher's "Introductions" to the dialogues, and Paul Friedländer's 3 volume "Plato: An Introduction."
The analytic standard is Julia Annas's commentary on Plato's Republic, and the Richard Kraus edited Cambridge Companion.
On the older "unitary" reading, see anything by Paul Shorey or Harold Cherniss on Plato (or the latter's books on Aristotle, which defend a certain reading of Plato against Aristotle).
For Neo-Platonist sympathetic readings, see anything by Lloyd Gerson or John Dillon.
For sorta-analytic, sorta-dramatic readings, see the books by Charles Griswold, G.R.F. Ferrari, Kenneth Sayre, and Charles Kahn.
For "mouthpiece" issues, see anything edited by Gerald Press or Francisco Gonzalez.
For non-Straussian dramatic readings, check out Drew Hyland, Mitchell Miller, Eva Brann, Kenneth Dorter, with Jacob Klein's Commentary on Plato's Meno being a kind of model.
For background on the Academy, see Debra Milker's book from the 90s, John Dillon's books, and Paul Kalligas's edited volume.
(Straussian, btw. Don't sleep on Stanley Rosen, a "heterodox" Straussian who taught several of the above non-Straussian scholars.)