Jessweeee♪, I'm with you there. Full elemental immunity is awesome. Plus by adding something like Flare to Elem-Def you can tip the balance into elemental absorption.

Roogle, there is an upper limit to how many types of spells you can stock. Of course for each type you can have between 1-100. I'll go into my old save and look up the numbers for you.

And while theoretically you can Devour your way out of needing to junction to boost many stats, it's not cost effective to do so (like in FFVII). You can easily beat the game without maxed stats.