That´s right, turning off the master switches is to protect the screens. I you start engines with Master ON sometimes you may see one screen or both go blank, the starters take almost all the power from the APU or the BATT. The RTU1 is powered by the emergency batt1 not by the main batt. The rest of the systems are not affected, just be careful to switch off the A/C or Heater before start up, you´ll see normally power up to 450amps on startup. Welcome to the nice Lear 60, next step is Rockets to Mars!!!