Comment - imbueing
I liked the Empire version of imbue, 'create spell-caster' It is very generous though and increasing its cost to 3 essence might be a reasonable cost for it. The mechanic of empowering to 1/2 of the casters INT was nice and would make Magical Champions of weaker Casting Sov's weaker but not overly so, as compared to similar Champions of more magically powerful Sovereigns.
On another note, 'create spell-caster' just sounds a little too ordinary.