It's an excellent idea Sakumo. I also like the ideas of having two of the elements be defensive and two offensive mainly. I do have a question about the minimum dks needed to begin this sort of training. I mean although jounin level seems to be the given rank, the seal can be acquired at that rank. I would like to suggest a higher rank than jounin, which would give people something to strive for. Also, the option of trying to master two elements at the same time, doesn't seem right, but as you said earlier the person trying to master the element/s is paying for it with hp damage so I guess its okay. Lastly, I although I agree with the idea of trying to make the elements even in power, I sort of had a change of heart as I continued to read the thread. It should hold true to the magna. But it won't effect the balance at all, because this is just a buff never to used in pvp battles.
Excellent idea Sakumo