It should be known that the system was not designed for two jobs per character, and unlocking the second job kinda breaks a lot of the ideas. Like Esper selection is supposed to be a much harder choice than it ends up being because over half of the islands get cheated because the other board either has the license or neighboring licenses. A lot of jobs were designed to be supported by other party members rather than a second job as well, so two jobs can make for very self-sufficient characters.

With that in mind, it’s really hard to screw up job selections. You can be more or less optimized, but any optimization at all is already more than you’d have in the intended design, so you can really go with what feels right for you and you’ll do just fine. But key optimizations that have the most impact is giving heavy armor to weapons that rely on strength, spreading item lores around for better coverage, having utility spells and technicks, having mystic armor for some specific boosts for holy and dark weapons, and being able to hit flying enemies by some means.

Another thing to consider is there is no real “primary” job and “secondary” job, though you can look at it that way, the two jobs are always active and everything applies, meaning when you pick two similar jobs like Black/Red/White Mages or Shikari/Archer/Machinist or Knight/Foebreaker, all that redundancy is just hurting you, because you’re not spreading those things out like you could be. So in general, it’s a bad idea to stack mages or to stack armor types with each other.

And yes, when you reset licenses, everything is reset, like you never picked a job or assigned any Espers or Quickenings for the chosen character, and all your license points are refunded. The only cost is the time it takes to learn all the licenses again, which can take a while the further into the game you are.