Excavate Protoss

This deck is meant to be a tempo board control deck which will ultimately lead up to winning with colossus. I’m not sure which way to go with a Mage Protoss faction, but I thought that the excavate package could add some depth to the deck overall. 

Current questions:

Is Void Ray needed? What would go in it’s place?

Is one warp gate enough, or does it need two even though there aren’t many protoss minions in the deck?

Does the excavate package help overall, or should it be eliminated for something else, such as a discover spell package?

Thoughts and comments are welcomed.