Idea: ST Cast on Crit GMP Arc Life Scion

The topic pretty much covers the basis of a build I have been considering for a while.

Gems would be:
4l: ST Cast on Crit GMP Arc
5l: ^^ + Arc
6l: ^^ + Arc

The build shouldn't require any specific uniques, but there are obviously some that would help a lot, so the build would be pretty inexpensive. The main reason I am posting this is to ask for help or advice on how to get this build going. I have a level 79 scion that may re-spec, or I may just level a new one, but without getting some final ideas down I don't want to devote much time or effort. Theorycrafting is another story, however.

Major flaw with the idea behind this build now: The point of picking scion is the easy access to life/crit/attack speed (for ST). However, I see no way to sustain myself with life leech or life on hit without taking a huge (1/2-1/3) dps drop. Any ideas?

ST GMP isn't an ideal conduit for trigger CoC unless the triggered spells benefit too, might want to consider a different trigger like Cyclone or Quill Rain.

If you build correctly your damage will be totally insane late game, dropping 1/3rd of your damage for a Life Leech gem shouldn't be an issue (although getting to that point where you're comfortable dropping an Arc is the hard part).

You should also consider going for Vaal Pact by the time you put in the Life Leech gem. Lightning Thorns and Ele Reflect will be your Achille's heel otherwise.