What is the range of this power? Does the spirit have to have been to the location it is gating to? As the Moon is moving towards having a Giasphere, could a spirit eventially appear on the moon from its plane?

I am pretty sure there is no such power. If you mean the ability to go through a shortcut in the metaplanes to appear somewhere: Yes, he has to have been there and needs to really KNOW the place. Otherwise a spirit can just travel on the astral or physical.

And if you mean the Astral Gateway power: That doesn't move anybody except their souls. It is just used for allowing a group to travel into astral/metaplanes, even mundanes.