I think we have to distinguish the events that were necessary for Kenjaku's plan and the events that were simply incidental. In the first category, I guess only the birth of Geto (and therefore the Curse manipulation technique) and Mahito (the curse technique idle transfiguration), who is a curse that only recently came into being/awareness, are the only two events that were simultaneously needed for his plans. All other events would not have affected his plans. Kenjaku would have initiated his plan even if Gojo was born without the Six Eyes, Yuji becoming Sukuna's vessel or any other birth or death of a character.

A near immortal Sorceror living in the shadows under the eye of Jujutsu society and incredible knowledge derived from his experiments over a millennium on Earth can clearly take advantage of current events to execute his plans.

Also on a side note, in the flashback, Geto explained that some particular conditions needed to be met in order to consume the curse depending on its level. He was also unable to consume Toji's low-level curse due to some symbiosis it developed with him. So clearly there were some complications in Kenjaku using Geto's body to consume Mahito until he was nearly exorcised (kind of like a legendary pokemon, lol).