The layout of the PCB is now nearly ready. I did clean up some of the traces and also did moved some vias out of pads. Now there is now via left inside a pad. The vias itself are also smaller now. Here are two pictures if the top and bottom layer:

The two inner layers are not shown, but there are mostly just two planes for Vcc and GND and not many traces.

I am planning to use OSH Park's 4 Layer service for a first prototype. But first there are some thinks to do:

• find a oscillator, crystal or resonator that is small enough
  (I think the size 2016 will fit, but not tested yet)
• Clean up both silkscreen Layers