what drivers do I need then
The driver on CD supplied with dongle DO NOT work with DVB-T Dongle
The driver provided by AirNav for microRadarBox DO NOT work with DVB-T Dongle.
For DVB-T dongle, install USB driver "Zadig 2.3" for Win 7 / 8 / 10
Download + installation instructions are here:
http://zadig.akeo.ie/after reading your antenna article is there an optimum cable length required (ie multiples of 3mtr lengths or....?)
No optimum length or multiple of anything, just random length as required, determined by antenna location and dongle/computer location.
Try to keep coax cable short to minimize signal loss in coax cable. The loss is proportional to length, longer the cable, higher the losses.
Cable length up to 20 ft is OK. More than that, you may need to add an amplifier to cover for cable losses.