Was covering the face obligatory for all Muslim women when the verses of hijab were revealed, or only for the wives of the Prophet? And how accurate is it that the Companions used to see the face of the suitor when he proposed?

A woman must cover her entire body from men. This is a general command for the wives and daughters of the Prophet (peace be upon him) and the believing women. The evidence for this is Allah's saying: "O Prophet, tell your wives and your daughters and the women of the believers to bring down over themselves [part] of their outer garments. That is more suitable that they should be known and not be abused. And ever is Allah Forgiving and Merciful" (Quran 33:59). And His saying: "and to draw their headcovers over their chests" (Quran 24:31). The women of the Muhajirun and Ansar obeyed this command and covered their faces. As for a suitor looking at his fiancée, this is from the Sunnah (definition) and is evidence that the women of the Companions used to cover their faces, because if it were customary to uncover the face, Jabir ibn Abdullah would not have needed to hide to see his fiancée.