Well it's at 0 because you're at max level....you can't earn any more exp points (in that class, at least).

Right now, the easiest way to get tomestones is to do Roulettes. Do all the roulettes. Also, do the Crystal Tower quests, they give a hundred tomes of soldiery with each run, I believe. Remember Poetics are still capped at 450 a week. Philosophy/myth aren't used anymore.

You can get the ponies everyone talks about in the extreme mode of the trials. If you just hit fiifty, they're a bit down the line in the story; you have to do the hard modes first.

Unlock level fifty dungeons and run them for loot you can unlock dungeons in Mor Dhona, playing the story, etc.

You should try other classes ASAP. Arcanist/conjurer has a few cross skills you may want as a BLM. You don't need to play if you like the one class, but it's good to experiment.