Fissure Help

Hi im kinda noob in poe. Looking for little help. Not sure what to upgrade next should I go for crit build? Get mageblood? Also have bit of problem with trinity in pob says it does not work when I slot it in. Im pretty sure I have enough cold dmg from gloves and passive annointed. Also have question about elemental weaknes from ballance of terror. I read that curse has to be casted manualy is that correct? Also does it activate if I just cast it even on empty ground or I have to cast it on mobs. I assume it last 10sec? I have about 150 div to buy stuff. Thanks for help

https://poe.ninja/pob/7a766

Forgot my merc have flammability curse on hit from ring. Ive seen there is helmet for merc that gives extra elem dmg but it cost like 20+ div is it worth it ?