Did Achilles know about his own vulnerability beforehand?

Yes, he did. When about sixteen years old, Achilles was summoned back to Phthia from the tutelage of Chiron. Achilles' father, Peleus broke the news that Helen had been abducted by prince Paris of Troy. read more

Achilles knew about this prophecy and for 9 years of the Trojan War, he dragged his feet. He was invincible in war but did not kill Hector. Then in the 10th year of the war, Hector mistook Achilles' best friend Patroclus as Achilles and killed him. read more

Achilles didn’t have any powers as you would describe as to that of a modern super powered human like Superman or Wonder Woman but as for his abilities : he was invincible/invulnerable in all spots but the heel giving rise to the phrase “Achilles’ heel” to refer to someone’s weak spot in spite of overall strength . read more

Achilles did as his commander asked and relinquished his bride. Then, he announced that he would no longer fight on Agamemnon’s behalf. He gathered his belongings, including the armor Hephaestus had made, and refused to come out of his tent. read more