hmmm, how about Wisdom for bonus MPs? Wisdom represents interneally learned natural instincts, and magic is more "from within" with EoM so it seems fitting to me.
How about you need 10 int + 1 int per 2 MPs needing to be spent for spells? (i.e. 11 for 2 MP spells, 12 for 4, 13 for 6, ... 20 for...