After temporarily giving up making my own Allstar microhub I opted to purchase a ready made one from G7RPG. It arrived today and simply works – plugged into 12V and it fired up and announced the IP via radio (subsequently I grabbed the MAC address and gave it the IP I wanted it to have via DHCP).
I ran an audio test on it fully expecting it to be perfect and it was indeed. So whatever I did when making mine is nothing by comparison. I shall investigate that at a later date but having a Pi in a box doing nothing has advantages as I am looking to make a GPS referenced NTP server.