You would need to add Mana Points to make spells have a kind of cost associated with casting them. MP would be spent casting and then recover over time... As usual. MP is based on Int and Wis.
Efficiency in spells can be gained just like with weapon skills, as a result the MP cost goes down slightly with each level of skill.
e.g.
Lev 1 Fireball: 30 MP
Lev 2 Fireball: 27 MP
Lev 3 Fireball: 24 MP
This way, experienced spellcasters can cast the spell more often and more powerfully. Levels can be gained just by reading, but not as fast as if you practice casting...
This spellcasting skill should also apply to Ischaldirh and his kin. They shouldn't just have random spell explosions appear here and there about them...
Proposed Spells (Most based on wands):
Fire bolt: shoot ray of fire in one direction
Ice bolt: ditto, a la Ice
Lightning bolt: Just like wand
Fireball: Same as wand
Create Door: Same as wand
Teleportation: Same as wand
Haste: Same as wand
Slow: Same as wand
Summon: same as scroll of Create Monster
Calm: like Taming, but only goes up to Friendly and only works on one monstet you choose.
Additionally, Ischaldirh and kin should retain their ability to disenchant armor and weapons, but it should require MP from them.