Could I get some critique on my Ice Nova build?

I'm not exactly sure what to grab for Ice Nova, but I figured mana regen, total mana, cast speed and elemental damage. + a few goodies on the way.

You don't even nearly need as much mana nodes as you've taken, seriously just scratch that. Especially mana on killing blow is horrible you just don't rely on this stuff.

Ice Nova requires you to stand right in the middle of the battle casting your Nova for which you don't have enough survivability especially in areas with high chaos damage you'll get bursted down a lot.

Make use of crit nodes, Freeze is amazing if you're going to play a frost character you need to abuse that.
And last but not least get a non AoE ability for bosses anything else will result in you struggling to kill high resi/regen rares.

I use ice spear for boss mobs.

I also use tempest shield and I am working on taking most of the block nodes that I can get to.

Endgame I want to use a rathpith globe to block spells also, might even consider a stone of lahzwar, but everyone has said to invest in critical, so I'm thinking of doing that as well.