I will attempt to help, digging into my (murky) past....
Q1. As per above. You can't fly VFR at night in the UK (Rule 22), hence SVFR inside a CTR, but IFR outside.
Q2. See the left hand side of the current CAA half mil charts (2171CD for example). Under the list of ATZs it says:
Outside the notified hours of operation of an ATZ, and at aerodromes without notified ATZs, pilots should:
a)endeavour to establish two way comms with the aerodrome
b)conduct their flight in the vicinty of the aerodrome in accordance with RULE 17...(all about conforming to the traffic pattern etc)
Certain bits of CAS, like the Solent CTR are de-activated when ATC isn't operating. See the UK AIP.
MATZs do not have ANY legal status. However you would be well advised to contact the controlling "authority" for a "clearance" to cross.
[Q3. ] Err dunno. Again try the UK AIP... failing that, HD? Or try ringing LL ATC up. They will help.
[Q4. ] A mystery to me as well. Up in Scotland they are useful as they give the military some idea of where the civil traffic should be, and where they should try to avoid unless they've got some sort of radar service.
Hope this helps
rgds BEX