I'm not of much help regarding the costume construction but I can say that I dig this idea! It sounds really cool/unique and still recognizable! I can't wait to see photos if you decide to do it!
Masamune Date - Sengoku Basara
Eren Yeager (casual outfit) - Attack on Titan
Levi (suit) - Attack on Titan
*~Next con I'm attending~*
FIN Desucon Frostbite (13-15 February 2015)