In a nutshell - yes.
VFR above cloud - no fixed figure but I reckon your own answer is what the lawers/CAA require. Take care though as gaps can soon disappear, good airmanship required here.
Night circuits would not normally require a flight plan and if your
night cross country didn't encounter any controlled airspace then an IFR flight plan is not mandatory. However you should request an IFR departure/clearance from ATC.
As I stated before the prime reason for IFR at night is obstacle clearance.
MOST commercial operations and some commercial training schools use QNH approaches.