a) In the quantities that I'm expecting to produce, long-tailed, straight-through, stackable female headers are too costly. As an alternative, I'm using separate pins (below) and sockets (above) by offsetting them by 0.1". This means that shields stacked on top are no longer quite directly above the base arduino. Is this an acceptable solution?
b) I've routed the GND pin adjacent to the AREF pin directly to the other GND pins. I did wonder if it was supposed to be a separate AGND, but I can't find anything to confirm this, so I've joined them all on the same net. Is this correct?
c) I've got a single, solitary prototype that works very nicely on my "parts-bin" home-made RS232 Arduino. My concern is that I may have duplicated assumptions made with the pin-spacing on my "parts-bin" Arduino onto the pin-spacing on my prototype. Is there anyone [in the UK] that would be willing to have a play with it on a 'real' Arduino? I've got some really simple test code to go with it.