I feel like you should do all the five temples, get the mastersword, find all the memory pieces to see the story, find the four great fairies, find all the towers to reveal all the map and beat the final boss ganon. The rest I would say is all optional, but try to find some of the best sidequests to do. I would not try to complete everything (like all sidequests, all gears, all legendary weapons, all korok seeds, all wells, all president signs, all monster camps, that kind of stuff, these are all optional imo).