I love the idea of a keys to success line.
As in the flame angel example provided, it would be useful to include anything to look out for regarding QT (copper sensitivity, etc.). Also if there are particular diseases that species is commonly associated with (uronema in chromis) or if particularly species are more seriously impacted by cyanide collection methods (CBB), that would be worth including as well.
Most fish dealers still list green chromis as beginner, but I don't think this is still true due to supply chain issues... which brings me to another suggestion. Instead of lumping them together, could we separate acclimation difficulty from care difficulty?
Copperbands, for example, are difficult to acclimate but I've heard in many cases they are quite easy to care for once properly acclimated.