Even before I finish reading, I'm going to say that having debuffs on monsters be affected by your spells would wreak havoc when you have two or more BLUs attacking the same monster, so that should probably be changed into self-buffs or at least somehow hidden from other players.

Having now finished, it sounds interesting and feasible for the most part. Unfortunately, I doubt the "star" system would make it into the game; the way data structures in databases work, it would probably require the kill count and target enemy tags to be applied to and then go unused for all skills on all player characters in the game.

Also, it is not my favourite take on the Blue Mage, but I will admit to being a little biased there :P