He is probably trying to add, somehow, coaches that teach his philosophy, consistently. Which I doubt the veteran NBA coaches do. His problem is that there aren't many coaches period that do. So he brings in a kid he taught himself who has aspirations, and some background in coaching.
A problem for Stevens may develop if the Celtic veteran NBA coaches don't buy in to his philosophy and just kind of diminish his creditability. Its one thing to get players to buy into your philosophy, its another to get veteran NBA coaches to buy in to it and teach it. "Your 36 a rookie to the NBA and totally delusional if you think think that your "Butler way" will work in the NBA". I am speculating, but I am kind of curious as to how much Ainge is letting him pick his own coaches. In that Stevens Philosophy interview Stevens kind of balked when he was asked something like, it must feel good to have some veteran coaches, and hear the Celts hired Adams. His response was to clarify that the final list of his coaching staff has yet to be announced.