The short answer is "No." There isn't a "minimum" of active powers required because these powers do not make him Thor. All of the "Thor" powers, characteristics and such are embedded in the Archtype that is Thor. When, by SFX, the Character wills himself to become Thor then he has all of the things purchased through OHID. Characteristics are inherent, powers are available for use, etc. He Just has access to all of these goodies that is all. pretty much if you knock out the normal before he changes that is the best way to stop Thor from ever appearing.