Advancement: By character class
which could be cleric, bard or druid depends on gods or maybe paladin or ranger for more war or battle orintated gods so any kind of class..
Spot is unnecessary because of blindsight.
Immunity to turn because they guard holy sites or temples.Turn Resistance (Ex):
Wardens have +6 turn resistance.
CR should be 7 because of spell like abilities, abilities and special abilities(aura andparalysis,trueseeing)
Resurrection and true ~ no work on undead.Unlike regular undead, Resurrection or True Resurrection effects do not affect Wardens. They have made their choice and cannot be returned to living form.