Healing is best done by potions. Clerics should use spells to buff themselves or the party or to disable the enemy.
Yeslick is better than Branwen simply because the is a fighter/cleric and can therefore hold his own better. He is also a dwarf so he gets the shorty racial bonus to saving throws vs death and vs spells.
Xzar + Wis Tome (Tome of Understanding) to be exact, but you can find one early on in Durlag's. I like to dual him around level 3 or 4, but you could wait until 5 or 6 for more arcane necromancy, but also a lot more down time.