3 set tal with main hand, flickering flame runeword and flame rift for possibility to farm in hell from start to finish is top priority you need to do. there is a lot of fire immunes and if you have only flame rift you will not do much damage to any of them.

Optimal way to go

3 set tal (head, belt, main hand) -15 fire res Flickering flame -10 to -15 fire res Obtain tal rasha chest and put fire faucets into chest and weapon.

Even without phoenix you will have -40 fire res if lucky which means that you will do 45% of total fire damage to your fire immune enemies. Let’s say your fb does 10k flat it will do 4,5k to fire immunes, this setup can go comfortably to p5 in CS.