are you trying to do the 2 herald trigger thing? its not possible anymore, they patched it.
It still works, just not as good.
I've been running up til this point with ice and thunder herald whilst shattering. Switched over to lightning spear build.
one more question came up - how do you know how much cold dmg is enough to trigger "Herald of Ice"?
I can't remember. I went through guides with this when I made my herald build. Just keep getting cold dmg on your rings, quiver, spec "Essence of the mountain" in your passive tree to help out, and nodes that gives you freeze build up. Worked fine for me. Used polcirkeln at lower lvls until I had enough passive points to make the freezing work without polcirkeln.
Keep in mind that it is important that you get cold dmg on both your rings and quiver if you want to freeze and shatter.
All though I highly don't recommend to run this build anymore since it has been nerfed pretty heavily. I LOVED this build before patch, hence I wanted to make it work this patch after the nerf, but it's just not as viable now. Too much struggle.