Magic is based on your character's level, but only accessible if the character has magic. So your MP pool will grow as you level up but how many charges you get is based on job class so for instance the basic White and Black mage will get more Lv. charges and the higher tiers are a bit low, but the upgraded Cleric and Magus classes have low MP charges for the Lv. 1 skills but get more charges for the Lv.8 spells than the original classes.
Also, your jobs Vitality stat does actually affect your HP Growth. So characters you stick to melee focused jobs like Monk and Viking will often have better HP than a character you consistently stick to mage classes, so make sure to switch characters around, so you don't have a dedicated mage character as they will have problems in the later stages of the game.