Male Kamui - JYB seems a little too obvious when it comes to playing up similarities to Lelouch
Female Kamui - ???
Dancer - ???
Ryouma - Kyle Herbert a.k.a. Kamina sounds good
Hinoka - Why not one of Saber's VAs or Mela Lee?
Sakura - Christina Vee is a good choice
Garon - in spite of not wanting the cast to be too similar to Geass, Michael McConnohie definitely knows how to play an evil emperor
Marx - I can't really object to the suggestion of Travis Willingham above, but I'm sure others would fit as well
Camilla - Besides those listed, perhaps Karen Strassman
Nohr's little sister - Yeah, Stephanie Sheh sounds right