Help my witch zombie summoner!

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For now, i'm also having problem with the high level gems while trying to stack iir.
Should I go iron reflexes or CI?

Neither. You cannot use Midnight's Bargain with CI and Iron Reflexes is too far away. You are better off just grabbing life. But since you do have the Cloak of Defiance, go for Eldritch Battery.

I like zombies in a +2 helm with multi, melee, and minion damage. Spectres are echo, FC, minion damage for me. Auras hatred and haste. All minion nodes (except shield cluster and instability). A rejuv totem can help immensly. Vall haste and vaal skels are both great for boss room. Flesh offering should be up 24/7. I use enfeable as curse usually because minions don't usually need extra dps.