PvE Cold + meteor wizard build

[The Lich]

0) Current updated version of my build:
http://imageshack.us/photo/my-images...hot2build.png/

1) You guys seem to be implying that it is necessary to have a signature spell in order to be able to cast my AoE spells even if I do have 12 AP Ray of Frost. Is that the case ?

1.1) If so, I found 3 signature spells that can help me regenerate AP. Which of those 3 is the best for my build (linked at the the top of this post):

Shock Pulse (Lightning affinity) to get +2 AP per hit it does on an ennemy
Spectral blade (Siphoning blade) to get + 1 AP per hit it does on an ennemy
Electrocute (Surge of power) for +1 AP per hit it does on an ennemy

1.2) If a signature spell is required, which of my current spells should be replaced by a signature spell ? (link to build at the top of this post)

1.2.1) With the new setup you suggested at 1.2), should runes from the other spells be changed ?