Thanks very much for that, and actually I think I've confused you as to what I am getting at so first of all I absolutely must stress that when it comes to 'business' I am absolutely understanding your needs and you have my sympathy really, cause it's a real mine-field.
It's not being infected by GPL that concerns me, I'm all for GPL. What concerns me software-wise is really only the uncertainty as to whether I would have to give-out the Axoloti sketch for my product. On the one hand, things I have read here and there accross the web, seems to suggest I might have to do that if I were to release my product commercially. On the other hand, frankly I think it might be complete and utter nonsense because if that were the case, then surely an artist would have to release the unflattened file if they were to commercially release an image created in GIMP or Inkscape, and a blender user would have to release their model if they decided to sell 3D prints of them.
So for that reason it all sounds a bit unlikely to me and I'm banking on the hope that I would not have to release my Axoloti patch just because the end product is released commercially. Releasing an Axoloti patch in software would be akin to what you are concerned about in hardware, so I am not surprised you don't plan to release manufacture-ready files of the board, Johannes never either, no doubt for the same reason - makes perfect sense.
So my only concern then with your own board is that you explicitly state the correct licence for it on release. If what you're hoping turns out to be true, and you are able GPL all of it, that's great, but whatever it is, you will have to be very careful and absolutely sure before you explicitly state its licence.
I would do more than speak to a lawyer, I would ensure that the advice given by them is in writing, to include they are accountable for any errors in their advice. Don't forget that one, it's a biggie and is often omited by slippery lawyers in order to escape accountability for the specialist advice you paid them for.