Thank for the advice but iam really a complete noob in modeling so ill need more explainations...
1- Non smoothered hard edges.
I really dont want my model to look more smooth or rounded, id like to keep it blocky, also i dont really see how smoothing the edges could reduce the vertices count...
2- UV Seam
Okay this could be a problem, for some faces i dont need to have 6 different squares, so i stacked them, but not perfectly, it basically looks like that :
are you telling me that each of them will count as a vertice somehow ?