Help with Crit Firestorm Templar Passive Tree

Hello! for Tempest league I wanted to try out Firestorm as my main skill. So far the DPS is doing OK in merciless but I feel like its lacking, I couldn't do maps most likely.

Right now i'm running a 5L firestorm with

Firestorm-FirePen-pCoC-Conc-Echo

I was using Herald of thunder but with Firestorms effectivness being so low the damage wasn't shocking often enough, more ele damage nodes would help with this I think.

I'm not sure how much casting speed really helps Firestorm as well.

Here is my current tree

https://www.pathofexile.com/passive-skill-tree/AAAAAwUABLMFQgceCPQJqg5IEQ8RLRGWFLAWbxo4GmwgbiSqJy8snDbpOlg62D1fQZZFnUbXSVFMLUyzUDBSU1NSVcZZ813yY_1o8mpDbRlxhXIPeuZ8g4IegpuD24hCi4yP-pBVlS6XlZf0mjua4J2uogCnCKyYrrPAVMBmwJrBxdD11abZ_Nte4XPjauQi6-7sGOw47TzwH_DV-d0=

Thanks for any help!