You can unequip your armor. You can run around naked if you want. I don't remember how to do it though, just look on the equipment screen and it should show a button that says unequip (triangle?). But yeah, never ever ever have more than 50% equip burden. You'll run slower, but far more importantly, it'll make your roll borderline worthless. Your roll will be slower, it will take longer to recover, and it'll have less invincibility.
You can get a wooden catalyst on 1-2, on top of the first tower on the bridge. There's another one in one of the jail cells on 3-1, and also on 3-1, you can get a silver catalyst right before the boss.
Generally, magic spells are more offensive, while faith spells are for support. Just depends what you want. I always play melee characters, so I only get the low rank spells in magic (like soul arrow and fireball) while I try to get as much as I can out of faith (heal, dispel, weapon echantments, maybe the spell that resurrects you upon death),