Hey guys. I am a returning player and advanced jobs were not around back when I last played like a yr ago. I just got my GLAD to 30 today. I want to be an effective tank for endgame etc. I am currently leveling CNJ to 15 to be able to start the quest for PLD. My questions are :

1. should I level CNJ past level 15? If so, till what level and for what abilities?
2. are there any other classes I should level? to what level and for what abilities?

Thanks!