Page 34&35 of the small rulebook.
Step 1- Declare action and spend AP.
3rd paragraph, 1st sentence says: "It is durring this step that the model declares a target."
Step 2- perform duels.
This is where you make the duels for the 3 (1)ap attack actions.
Step 3- resolve results.
This is where you deal the damage from the attacks.
You dont go back to step 1 because the action has not been resolved untill you make all 3 attacks.
In the box "actions causing actions" it says "the original action is not considered resolved untill the new actions are also resolved.
So the way I read it, you declare "flurry" as your action. Spend the 2 ap and a card. Declare your target. Then you make 3 attacks with a cost of 1 ap against that model. Since flurry is your action and not the attack actions themselves, you only target a model once.