Finally we routed the board. This is the first time we designed a PCB so please forgive any blunders. Managed to squeeze all 3 SPI sockets for potential extensions like pressure sensors. We can already think of some crazy applications.
We also have sockets for battery and buzzer connections. This way there is no need to solder anything, just plug&play.
Eagle files can be found here.
Now it is "just" off to the manufacturers to order the board and component suppliers to source the parts and we are ready for soldering. Hope all is properly designed :-)
Phase 4 - DONE.