I've made some changes to improve manufacturability:  

• The Arduino Nano has been eliminated; the bare-minimum components for equivalent functionality are now integrated into the design.
• The through-hole load resistors have been replaced with arrays of 1206 SMD resistors that I think will better be able to dump heat into the board.  
• I've added M3 mount holes to better facilitate mounting in an enclosure.
• Since the Arduino has been removed, we need to find some other way to power the board.  You have a choice: the AVRISP connector (provided to program the ATMega328) or a USB-C connector (because all the cool kids are using USB-C for power now :) ).

Extras may be available for purchase once they arrive and are tested.