Priests are similar to the Magic Drummer in that they have no attack. They only will heal the unit with least amount of soldiers, so it's essensial that all of your units are same level, otherwise your Priest could be trying to heal a unit that it healthy only because it's of lower level and has less troops. The Spring Ode skill heals all units. Priests morality bar increases only when they are hit by an enemy unit. It should be clear that Priests belong either in the 2nd or 3rd row with defensive units in front to protect them.
Enchantments take a varied amount of Enchantment Cards depending on the level of your Hero. The higher your Heroe's level, the more cards you will need.
Note: Priests have no offensive enchantment.