Ok, to answer some questions. The footage from Flashback is inconsistant. In some frames, the Neo-Nupetiet-Vergnitzs Bis is shown in front and in some frames behind the Megaroad.
The main reason for me to say it's that large, is firstly, that it is drawn in the schematics next to the bis. I would assume it was to scale, it would make sense. Secondly, this image:
Shows a massive city. Those lines are either highways or monorails of some kind. Those aren't really skyscrapers, they are more like arcologies! This ship is massive. It WAS constructed on the moon, and probably flown to earth for the ceremony. On earth it is in a dry berth, not water, though I imagine it's quite capable of floating.
The top ships on the back probably fill the daedelus role of the ship. I'd imagine they all can detatch. The schematics show pretty well the engine block for the neo daedelus craft and the twin engines of the ARMD craft. Yes it's a large ARMD craft, but you're forgetting some things.
There is 80,000 civilians onboard in teh city, however, that's just as of 2012. With the breeding practices after SWI (Basically, citizens are encouraged to breed like rabbits), expansion would be expected to occur expedentially. The city is much larger than need be. It is also large enough to possibly house some full size zjentohlauedy.
The ARMDs not only need to carry mecha, which includes only several hundred VF4s, but probably twice as many VF-1s, and auxillery craft - SFs, QFs, shuttles, etc.
It IS an ARMD. It is shown to be that way in Macross M3.