Ice spear Burn Mara

Hi Forums,

currently theorycrafting an ice spear burn marauder. AoF + the new Cold to fire are tempting me! ^^
Core skill:

Ice spear + Cold to fire + Inc Burning damage + Ele Prolif + (Crit Multi)

Tree would look something like this:


I know I wont reach 119 Points but thats the core I want to build towards.
Summary:
189% Fire damage
105% Burn damage
100% Elemental Damage

In its seccond form I dont need more Crit than I get from gear for the spear to almost allways crit. I also dont need aditional projectiles, Proliferation should be the source of AoE.

Also Herald of Ice will ad aditional base damae to the spear.

What do you think of this? Viable? Also What defense Options do you suggest?
I thought about a high level Frost Wall with inc duration and echo to lock everything in place while the burning action takes place.

Really hoping for input from you guys here.

regards