Today I found the time to finish the design and export the Gerbers in KiCad. 

Learnings:

• Gerber export is done via File->Plot in PCBnew
• Solder mask min width had to be set to 0.099 mm to allow 0.1 mm solder mask bridges between the codec pads (found in Setup->Pads to Mask Clearance)
• Looks like castellated holes leads to extra charge due to special milling bits