I finally went with the opera singer. I will wait for the videos on texture and patterns before going further. 

Here are the sketches I did. Excuse the use of french words. As french is my native language it's hard for me to "think" in english.

According to me those 3 ideas are the strongest...

I did some color tests this morning. I was about to post the progress that was looking like this :

 I receive a mail from Behance telling my that one of my illustration have been added to a collection. I had a look to that collection and it's owner. Surprise ! I find this wonderful illustration of Julia Solans :

Oups... I'm gonna choose another concept ;) I will go with the opera singer ! More tests colors to come...