Any Dynon bus cable length would do, functionally you could use a 6' cable, if that is easier for your cable routing. Only depends on your panel layout. It could be that you want to be able to unscrew the Dynon unit and be able to move the unit out of the panel so you can reach the back an undo the connectors. I made all my cables from scratch so I just picked a length that allowed we to conveniently route the cables behind the panel. If your knob and comm panel are mounted close together then a 6" cable could be more than long enough, but it all depends on the layout and the routing between the units in the panel. There is no required order in the Dynon bus wiring between Display (with two plugs), Knob panel (with two plugs) and Comm panel (I don't know how many plugs). On units with two plugs the plug are identical and they are just provided as a convenience so that you don't need that many (if any) network hubs, the only requirement is that there is a path (through as many intermediate units as you want) between any of the units on the Dynon bus (they call this party bus in the installation manual)