Regarding minimum crew; an excerpt from UK's CAP393:
Pilots required on public transport flights by helicopters of 5700kg or less
46 (1) Subject to paragraph (2), a helicopter registered in the United Kingdom must carry at least two pilots as members of its flight crew if it:
(a) is flying for the purpose of public transport;
(b) has a maximum total weight authorised of 5700kg or less; and
(c) is flying in circumstances where the commander is required to comply with the Instrument Flight Rules or is flying at night on a special VFR flight.
(2) A helicopter described in paragraph (1) is not required to carry two pilots if it:
(a) is equipped with an autopilot with altitude hold and heading mode which is
serviceable on take-off;
(b) is equipped with such an autopilot even though before take-off the autopilot is found to be unserviceable, if the helicopter flies in accordance with arrangements approved by the CAA; or
(c) is flying by day and remains clear of cloud and with the surface in sight.
As mentioned before, VFR by night in UK doesn't exist. So two pilots must be carried by night in a non-autopilot equipped helicopter, irrespective of the number of engines it has.
The "floppy sticked" police helicopter I flew ten years ago would no longer be allowed to operate for that purpose by night because we could not carry two pilots.