Go read this. It is as thorough dive into what Kirby Smart's defense will be and how he will approach the philosophy of defense, as opposed to the formation or on field stuff. He also gets into his approach to day to day coaching.
The one thing I'll add, and that we are seeing in recruiting, is the focus on finding the atheletes to successfully run that philosophy. Because no matter how good your philosophy is (think Mike Leach's offensive view), if you don't have guys to execute it, you are still just an average coach.