If you're playing Premium, spend the 300 points total to unlock all 3 cauldrons. Then take a decent weapon for Rick, and do 3 full upgrades. (I only did two, cause I'd already wasted the first one on Yamato.)
Rick is a total tank; most enemies only do 1 damage even on hard mode. So with a weapon that has an extra +50-60 ATK from the cauldron, you can just about Auto every battle and not even care if the other 2 members die, because Rick will always win!

P.S. You can also add more slots to his weapon so he can equip 4 crystals if you want to.
EDIT: I forgot to add, buy 1 storehouse key so you can enter the storehouse in the first town. That'll get you the Well-Maintained Fur that makes Rick so indestructible!