It is a magic spell from Mage: The Awakening. As for Space I mean area the definition of space regarding area or place.
In that case stick with "
spatii"
As for Da mihi potestatem; I have had no other objections to its usage from anyone else in the context of a magical spell.
I don't really think it is fitting ...
potestas means "power", but more like the power you have as somebody's master/ruler or as an authority
Metonymically, it can also be "power to do something" in the sense of "opportunity to do something" or "permission to do something", but that's not what I think of when I think about the power you obtain from a magical spell.
I like
vis because I have read it in the context of divine power or the power of nature and other abstract phenomena, so I think it would also fit with a magical context.
I won't prohibit you from using potestas, of course.
You can just exchange "
vim" with "
potestatem" (and vice versa) without having to make any change to the rest of the sentence