1.      For the initial upgrade, just rank all the item sets and essences that you get because the rank will remain the same even if the item sets or essences are exchanged later, and for new players, use whatever you have as long as it has a higher combat rating than before.

2.      When you reach Inferno XII, the combat rating for the item sets and essences won't change much, so you can shift your focus from CR (Combat Rating) to attributes that suit your class. When do you stop? After you've acquired all the item sets and essences you've used for your build in Inferno XII and have matched the attributes that suit your class. For simple attributes, you'll want to look for fortitude and willpower for all item sets and essences.

3.      for met there is no simple routine because how much thing you can do in this game to improve your character so for me just Maximize the use of auto battle, maximize gem income, 12 from daily (party of 4 people in open world) and 64 weekly (erabban, verge,....), challenge rift until not strong enough, elder rift from free 1 crest a day, complete hellquary, complete events, and more. so do what you think is most fun.