Question about Master Levels & Beginner Endgame Progression

Hey! I'm a returning player, coming back after a 15 year break lol. I've got some friends that I used to play with back when I was in high school and we decided to all come back and check the game out and we are all addicted. I just hit lvl 99 RUN and have my BLU at lvl 50 because I want to play tank and I hear that /BLU is the best tank sub. I'm looking on the wiki about master levels and it says that it allows my subjob to be a higher level than 49. Does that apply to the job I master when I set it as the sub? Or does it apply to any sub when I have the mastered job set to my main? I can't find any clarification online so I'm hoping to get an answer here. Thanks!

Also, we need some help with advice on what endgame event to start for our next progression after the sparks gear. We are not finished with the story missions for any expansion, we only did enough to finish RoV. Should we hard focus all of the missions for all expansions next? There is so much content in this game with Dynamis, Ambuscade. Odyssey, Sortie, Reisenjima, we are feeling insanely overwhelmed with content and what we can and can not do with our squad. We have me as tank, a SAM/DRK dps and a WHM/RDM healer.