After a small revision to the board, I finally ordered it on OSHPark. The revision includes a new stereo pot to control headphone and speaker output volume. I changed the micro USB SMD connector with a through hole mini USD because I had to resolder the SMD part multiple times. Finally I added the possibility to have a functionnal board without optional speaker/amp and battery parts.
Once populated and soldered I discovered that I can't get the initial firmware to work... I originally used mbed but after trying for some hours I couldn't get it working. I imagine that I changed something in mbed directly but impossible to find it out. So I decided to change platform from mbed to libopencm3 plus atomthreads and make a new firmware (almost) from scratch. It was actually a great experience which take only a few hours and new firmware is better than the original one.
New firmware and Eagle schematics and board design are available on a new github repository.