>>2953465
>>2953484
>>2953485
I did a ground fill on the front and back sides and the DRC didn't complain that anything was unconnected, so I think I can get away with it if I scatter some vias here and there to join the front and back ground planes together? I will also add dedicated ground returns for a couple of clock signals, and also the top right IC communicates via SPI so that's why it's as close as possible to the connector pins.
I will work on the silkscreen now, I won't be able to fit component values and designators so I think I'll just have designators under the footprints.
The idea is that 4 of these will plug in to a baseboard with pin sockets that I'll make from strip board.
I'm not sure if this looks overly ambitious, especially for a first attempt. I have breadboarded all this though, and it does work.