A ninja is basically anyone who has graduated from an academy (though not necessarily) and are capable of using their chakra in a way that allows them to perform jutsus.
Physical energy is basically kinetic energy, which is the bedrock of Taijutsu. Coupled with spiritual energy, they form Taijutsu.
As for categories, I'm not sure. My bad about the delayed reply - replies will be a lot more frequent from now on.
Priest listen to the student's short explanation but he's far from satisfied. He would punch a tree, shattering it to bit with overwhelming force. Then he'll face the student once again.