Is it understood from the hadith that the Prophet knew of his death and had chosen his successors beforehand, and how does this conflict with the hadith: "You are to me as Aaron was to Moses, except that there will be no prophet after me"?

First: The hadith (definition) "Follow those who come after me, Abu Bakr and Umar" does not mean that the Prophet, peace be upon him, knew the time of his death. Rather, it is like the recommendations people make. Surat An-Nasr was the last surah (definition) to be revealed from the Quran, which indicated the approaching end of the Prophet's life, peace be upon him. The Prophet, peace be upon him, was given a choice between this world and the hereafter before his death.

Second: The Sunnis differ on the caliphate of Abu Bakr, may Allah be pleased with him, whether it was based on an explicit text or on indications that the Companions inferred, and then the pledge of allegiance and consensus were established. The Sunnis have unanimously agreed that the caliphates of the four Rightly Guided Caliphs were valid, and their rank in virtue is the same as their order in caliphate: Abu Bakr, then Umar, then Uthman, then Ali.

Third: The hadith "Your status to me is like that of Harun to Musa" does not contradict what preceded. It means that the Prophet, peace be upon him, appointed Ali, may Allah be pleased with him, over Medina, just as Musa appointed Harun over his people. It does not mean that he was the caliph after him. It has been narrated from Ali, may Allah be pleased with him, that he said: "I will not find anyone who prefers me over Abu Bakr and Umar except that I will flog him with the flogging of a slanderer."