In case anyone is interested, in answer 2, this is straight from CAP 413:
2.13 When transmitting messages containing aircraft callsigns, altimeter
settings, flight levels (with the exception of FL100, 200, 300 etc.
which are expressed as ‘Flight Level (number) HUN DRED’),
headings, wind speeds/directions, pressure settings, airspeed,
transponder codes and frequencies, each digit shall be transmitted
separately;