2014-11-24 You can target any player with Abzan Advantage, even if that player doesn’t control an enchantment.
2014-11-24 The enchantment will have already left the battlefield when you bolster 1.
2014-11-24 Bolster itself doesn’t target any creature, though some spells and abilities that bolster may have other effects that target creatures. For example, you could put counters on a creature with protection from white with Abzan Skycaptain’s bolster ability.
2014-11-24 You determine which creature to put counters on as the spell or ability that instructs you to bolster resolves.