What do you guys think of a couple new spells for Clerics and Mages. The mage armour spell would be called Mage Armour and would increase mana regeneration by X% (level based) and cast only on self. The Cleric spell would be called Stone Shield and would raise armour values by X as well as striking back against melee attackers with X damage. Self casting only. I also think that armour spell should be considered for lvl-based increase. I'm not thinking a huge increase, but maybe max out around -40 ac with a top-notch caster.

I like your idea of making armour level based and have a cap on it. About mana regen i would love some but dunno if that could happen. And stone shield sounds a lot like fiery vortex. Maybe more like spiritual shield when u repel some magic attacks deflecting power , like -5 saving spell or stuff like that.