Is it possible to display a breakdown of types of entities in the area? I know that the current count is provided based on debug, but is there a way to break out how many are, for example, hostile, neutral passive? Would help a lot with spawn proofing (when you don't care how many bats and fish there are).

There is a mob cap info line, but I think it's currently only in the 1.12.2 version. It will be coming to all the version at least when the 1.12.2 code next gets ported forward after the mod rewrites are finished.