Two final boards are done by now. One with crystal and one version without crystal. The version without crystal also breaks out the 2 crystal pins to the breadboard.
All components are on one side and are big enough for hand soldering with a pincer and small tip soldering iron (at least; that's how I made the boards in the picture).
Both ends accept a 6-pin USB/Serial (FTDI) programmer adapter, so you can configure the 328PB for a bootloader on UART0 or UART1, and have a serial connection on the other UART.
Or use two serial adapters at the same time and program via the ISP connector on top.
While the board is backwards compatible with the Nano-V3 footprint (except 3.3V pin) it has no built in USB.
For future readers who want this:
Attached are the Eagle boards files, that can be imported into Diptrace, Kicad, etc.
Eagle board files.zip (19.9 KB)
Parts list:
1 x 0805 SMD Led
3 x 0805 SMD Capacitor 0.1 uF (2x for DTR reset line, 1 for mcu decoupling)
2 x 0805 SMD Capacitor 10 uF (for AMS1117)
1 x 0805 10K resistor (for reset pullup)
1 x 0805 1K resistor (for led)
1 x AMS1117 5V regulator
50 Pinheaders
and for the crystal version:
2 x 0805 SMD Capacitor 22 pF (anything from 12-22 pF should work)
1 x 16MHz crystal
Good luck!
Hans