Ghost Reaver Vaal Pact

For this as my main build spell caster, is it better to go with Witch for more of the spell caster passives or go with Shadow to get to these abilities better?

If you want to go CI it is better to start as witch because of the ES passives at the witch start.
I recommend going for a life build as a beginner though. It is much easier to level as the gear pool you can choose from is bigger (life mods can roll on all gear pieces, whereas an ES based char has to avoid pure eva and armour gear for the most part).