Hey kashah, thanks for your thoughts.
The annular ring thing is just because those pins are connected to the (solid) ground plane so there is copper where there would normally be resist. I am not really aware what a "thermal relief" does or why you would use it... could you explain?
I will have to fund manufacture personally, so mistakes aren't welcome, but most components are relatively cheap; the most expensive is ~£12. I'm hoping to get a company to assemble it, as I am not skilled in SMT work and this is pretty small (circa 3x2").
The one thing I am pondering is making a "model" of the pcb to check that the headers and outline will actually fit on the beaglebone. I have access to a simple CNC machine, so wondering if there is an easy way to turn the pcb outline + holes into something a CNC package could use?
I'd be welcome someone looking at the project files, but am unsure which files to package and how to make them available here... would the kicad_pcb + .pro + sch files be sufficient or would I need the other libs and stuff too?