By the way: I meanwhile have a pick and place machine and improved the design which I populated here.
So if there is interest I could produce some of those boards ....
I had some of these boards made and soldered one up and I'm happy to report it works. I have to finish populating the PCB, but all looks good, bootloader flashed and the small USB 2x2 app loaded, no problems so far. I have yet to located a suitable SD card holder for the PCB, I have a few coming in the mail though.