I basically did the same. My MC had high magic, high vit, and average agi. You'll want to get at least 15 agi for a caster, so you can get the elemental Jumps (1.5 damage for that particular element. They don't stack with the elemental Rises). You don't want your agility to be absolutely abysmal as well, because you're mote likely to not get any extra turns (even if you crit or hit a weakness) if you always go last. I finished with 17 agi (and like. 30 magic and 28 vit or something), which makes you fast enough to get extra turns half the time. It also means that when enemies attack you, you'll have a pretty good chance of wiping them out as well, which cuts down on your battle time.

I generally don't pay attention to weaknesses, so when I suddenly see WEAK pop up on my side, I'm like. Oh shi- I have a similar mindset as well, so sometimes it was fighting an uphill battle when the only person on the battlefield who could revive... got killed. I ended up having to summon a demon that was 20 levels underlevel to revive the guy SIGH.