Help with stormbrand build

Hello everybody.
im trying to make stormbrand-critical strike witch/elementalist/may be swap to occultist.
The main idea is abuse "choir of the storm"//over lightning resist gives critical strike bonus + its gives solo target dps boost.
(near 42k dps only from amulet and lightning damage passives)
As main body i dont use carcass,im using shroud cause im not tanking mobs and dont use brand recall often.Usually im recasting brands->"the shade form" proc more often.
I killed red elder,it was easy.

i have near 4.5k hp +1.2k es.(chance to evade 22% and dodge attack 12%)

Bosses not problem for me.only syndicate smt.

Main problem is Alva on t15-16 maps,when i meet a lot of creeps with long attack range->they oneshoting me.

How i can boost my surive ability against them?
Why i dont take acrobatic -> its too far//i can take it if i will play with overload,its gives a lot of free points,but its another build.

About flask:
Blood is karui(best hp flask - my opinion)
Vinktars vessel ->giving me +50% crit chance,flat light. damage and lifesteal
Aziri -> dps+lifeleach
Lavianga->mana cause im using MoM
Crit.chance flask with freeze immunity.(i need freeze immunity and im crit build)

P.s.Sorry for my English.