The fact that Providence is the force behind Nemesis and Insight the one behind Little Death is a result of their functions. It should be noted that Nemesis initially worked in Providence's department and was later on transferred to Insight's, which led to her internal and external growth. Nemesis aka retribution that is based on realization is inherently more stable than if it is solely based on the urge of revenge alone.
As for Little Death: In my mind, I always had him have a very juvenile, but also a distinctly black voice. Until now, I've never seen an opportunity of actually showing it, because he has no visible face. The fact alone that he's wearing a hip hopper's hoodie may have been the only hint.
And our middle aged grumpy, highly organized boss and head of the High Council is not only Coincidence, he is also his own mischievous underling, the wise cracker.