The most important stat is cast speed. This should be on every available slot and you should try equiping exalted cast speed whenever possible.
Slow is needed on the weapon for Trapper 3/3.
One source of frailty should be in the build. The best slot is amulet followed by Curse of Sulphur and then finally the relic as a last resort.
Minion damage and minion health can be added in any slot shown below. There isn't any preference between the two.
Legacy of the Quiet Forest is the only unique that is "required." The build will function without it but it is a massive quality of life improvement and should be targetted with runes of ascendence if you do not have it.
Doublet of Onos Tull is a legendary option. It is not recommended to use unless you get one with SuffixIncreased Health because it will drastically reduce your defenses with just the base item.
Remember to always cap resistance (75%), endurance (60%), and critical strike avoidance (100%). Use as many implicits and blessings as you can to do this to leave room for health on as many suffixes as possible.