The cleric takes 9 damage
To start with, resistance takes effect after all other damage reductions. So the 24 damage is reduced before resistance is considered. This rule can be found in the Combat chapter of the Basic Rules:
Resistance and then vulnerability are applied after all other modifiers to damage.
After the damage is reduced to 18 (Xd6 = 6 in this example), it is halved to 9 from the resistance granted by warding bond. The cleric then takes the same amount of damage:
each time [the target] takes damage, you take the same amount of damage.
Ancestral Protectors would not affect a target you hit before entering a rage
You can take bonus actions before actions in a turn but this does you no good because your bonus action, activating rage, would prevent you from casting booming blade.
If you instead cast booming blade first, which includes making an attack as part of casting booming blade:
As part of the action used to cast this spell, you must make a melee attack with a weapon ...
You get to the heart of your question. Ancestral Protectors says:
While you’re raging, the first creature you hit with an attack on your turn becomes the target of the warriors...
Most people would probably read "hit" and understand it in the subjunctive tense. That is: you must first be raging and then make an attack for the Protectors to take affect.
However, out of context, the sentence also makes sense if you read "hit" in the past tense. That is: when you activate rage, the Protectors affect any creature that you already attacked that turn.
The problem, if you use this second interpretation, is that the past tense would not make sense after the first turn when you entered the rage. You can't be talking about a triggering attack in the past tense when haven't made an attack (say, at the start of subsequent turns). So you have to understand the sentence in the subjunctive mood and that means the attack must come after the rage is entered as a bonus action.
So booming blade won't work with Ancestral Protectors. Further, the Protectors would only affect a creature you hit with an attack resulting from action surge if your normal attack action produced no hits.
This answer is incorrect.
It was written with the assumption that the OP was quoting the rules text from an official source which, it seems, they were not.
The official text for the ability is "another creature you can see" not "a creature you can see." In fact, even the lead rules designer Jeremy Crawford made the mistake of assuming the "a creature" wording was correct in his tweet below.
It's comforting to know that even Jeremy can make this mistake but the fact remains that ANOTHER creature must be the target of the Barbarian's ability. See my second answer instead.
I can't delete this answer because it has been accepted so, I'm editing it to put this disclaimer in until it can be deleted and leaving the original answer below for archival purposes. My deepest apologies for the damage I have cause by answering incorrectly.
Yes, the Barbarian can benefit from his/her own Spirit Shield
Even though Spirit Shield is an ability not a spell, the rules on spellcasting talk about a parallel situation with (spell) effects:
Assuming the Barbarian can see himself, he can target himself to benefit from Spirit Shield. Of course, the flipside of this is that Spirit Shield would not be available for use on an ally until the next turn, so doing this does have an opportunity cost.
There may be circumstances where the Barbarian cannot see himself: if he is blinded or in the dark for example. But otherwise, your interpretation is correct (and has been affirmed by Jeremy Crawford in an unofficial tweet).