SO! It's finished! I tell you it was so long to make that it's going to take a little time before I want to see it again (and thus wear it^^).
I'm happy because it was good practice for my sewing skills: I made a correct peplum, I managed to sew slippery silk for the lining and the snap placket is well done and hidden. But there's still the fit issue at the back even though I altered the pattern and checked regularly how it was going.