Yuval: Thanks for the Mansfield suggestion — I’ve read a version of it in this book, which doesn’t include Burke’s letters but is an excellent (and affordable) volume on political philosophy in general. As for biographies, it seems to me that anything written before the release of the letters is only the start of it. There’s also the critical work of Peter Stanlis, Francis Canavan, and Russell Kirk, who fundamentally reoriented understandings of Burke.
Somebody should take on this important conservative project: a new, popular biography of Burke for the 21st century.