If you will go hirez and sculpt on it anyway, then I'd go into ZBrush (gotta fix n-gon first though). Just that you would have to do a new retopology once the hirez is done.
HI everybody ! Huge thank you for your feedback ! I didn't expect that. Your advices are really handy. I modified lots of things (and i made lot of screenshot !) The headmesh is a basemesh i find on "makehuman", i thought it was better to sculpt it on a soft like zbrush. Here is the results :