Elemental expression interaction

Leopold's Applause jumps to mind, because you'll want to scale penetration to amp the damage more. Getting Trinity for the independent damage multiplier would also seem like a good idea.

Apart from that, if the shockwave totems are triggering EE then you'd want A. as many totems as you can get and B. make them attack as fast as possible.

I'm also spying that EE has an internal cooldown of 0.25S. That suggests that slotting it with ingenuity and as much CDR as you can manage would be key to scaling it alongside the totem's attack rate.

To finish up, seems like EE scales mostly like a spell. That means getting an amulet with +3 to spell skills would scale this massively since it gives 9 spell levels to EE cuz last I checked it triple-dips from "All Spell Skills" stats.

I'm not sure if you're able to get giant's blood with this setup since it's pretty far away on the tree, but I can see that Quecholli only has an 88 STR requirement. It should be reasonable to get that much STR, which would enable the use of Crest of Ardura (for tons of CDR to proc EE more) or Sunsplinter for a further +6 gem levels. My intuitive guess is that Crest of Ardura is worth more damage for less mana, since CDR is not common on gear.

Either way, EE is going to cost buttloads of mana. If it starts to be prohibitive, I'd probably stick it on lifetap and/or inspiration to manage costs.

If you have spare spirit leftover once you've handled all that, I'd be looking at whatever you could slot into cast on crit. This build is probably doing a truly insane number of crits that would let you blast off even more spells.

See what you can manage to pull together in terms of pathing. If you get a PoB link to me with some basic pathing that handles the above ideas, I could refine it. Past that, your main vector of scaling is spell damage and elemental damage, as you pointed out.

I am trying to make use of Elemental Expression myself, though I went for a spear - Tangletongue crits all the time. If you are able to grab Giant's Blood to grab your mace in one hand you could try item combo I am using right now. Threaded Light focus give spell damage scaling with spirit and Invoker has easy access to lots of spirit on higher levels. If you equip Crown of Eyes with that you can scale both Elemental Expression and other attacks that way. I don't know if attacks scaling affects totems though.

I would seriously consider looking into crown of eyes to allow spell damage to scale the skills you're using to trigger EE. I helped a guy out with a spear & focus build idea but the aftershock and totem application method sounds cool.

EE triggers at most 4 times a second, maybe slightly faster with cool down reduction or quality from fox talismans? Are you seeing more than this? I'd be interested to know if totems somehow have their own icd. If that's the case, EE itself scales way harder with a totem strategy than anything else and it's not close