IIRC but no POH here to hand is that you HAVE to use the mains for take-off and landing, not the wing tanks; that makes a bit of sense too as there are variants for the DR400 which only have the mains tank - no wing tanks nor the auxilary fuselage tank.
Re Nose Gear; the steering engaging/disengaging mechanism is a purely mechanical affair; nothing to do with the strut air/oil bits, although a low strut due to lack of air/oil will make the symptoms described worse; not better.
But happy to stand corrected as I know nothing.
