Poison Spark Elementalist, Need Advice

Hello! I've been playing every weekend since league start and I just picked up my 5th Exalt from the ground, so during my work hours I've been brewing this Poison Spark build:

https://pastebin.com/N0Szq2i9 <-- Original 4k Life + 96% Stun avoid version https://pastebin.com/xeARw841 <-- Newer 100% Spell Suppress but 3k Life + 40% Stun avoid version

Concept

• Ashes of the Stars can give up to 30% quality to all gems, and +1 level to all skill gems.
  • 20% Quality Phantasmal Spark now converts 100% Lightning Damage to Chaos
  • 20% Quality Divergent Herald of Agony now grants 70% Chance to Poison on hit
  • 20% Quality Anomalous Withering Step now inflicts 12 stacks of Wither (7 stacks from Level 20+1, plus 1 per 10% quality)
• Circle of Nostalgia can have 50% Herald of Agony Buff Effect, pushing the herald's Chance to Poison on hit to 133% (not sure how PoB computed that).
• Shaper of Winter makes Spark still Shock so that it would still activate Herald of Thunder.
• Level 21 Herald of Thunder on a Crest of Desire can get up to Level 30 that deals Double Damage.

Pros

• Map Clear: Between Spark, Herald of Thunder and Double Obliteration explodes, I don't think this build will encounter any issues mapping aside from Reflect mods (deactivate Herald of Thunder when the map has an ele reflect mod).
• Budget: The shopping list below can be obtained with a small budget of 5ex, which is great for a second character after a successful league starter.
  • +8 Crest of Desire: 1ex
  • +30% Ashes of the Stars: 1ex
  • Circle of Nostalgia (any% buff effect + 60% chaos damage): 50c
  • Brutal Restraint: 20c
  • +20% Phantasmal Spark: 40c
  • +20% Anomalous Inspiration Support: 100c
  • +20% Divergent Herald of Agony: 40c
  • +20% Anomalous Summon Stone Golem: 40c
  • +20% Anomalous Withering Step: 40c
  • Everything else is between 1c and 10c (aside from a Watcher's Eye, which I only use for Chaos Resists..)

Possible issues, need advice

• Untested build: All of the above have been brewed "on paper" only and I want to get advice before committing on it in-game.
• Mana issue: I'm running Eldritch Battery + Chaos Mastery leech to ES, but I haven't tried it if it's comfortable to play without Mana Flasks.
• Single Target damage: I'm not sure if Spark can deal enough single target damage on its own. PoB tells me that I can deal 1million chaos damage without overlaps (during Convergence), and if the Arena is small enough (or if the boss parks themselves in a corner), the overlaps should be enough to kill them.. or would it?
• Survivability: On PoB, I have 4k life on level 100, which means I'm probably going to have 3k life on endgame. I also have Primal Aegis, Elusive, 43k evasion, capped Resists, elemental ailment immunity via Purity, Corrupted Blood immunity, 100% avoid Bleed and Poison and 96% avoid stuns. However, I only have a Stone Golem for life regen, negligible attack block and armour, no spell block and no spell suppression.

Any advice is appreciated, please help me polish this build. Thanks!