Dog won't freeze ,the aft cargo hold is heated by air from the passanger cabin.It's not so warm as fwd cargo hold,which is heated directly by airflow from electronics..
13. in flt ,both igniters activated.The spark is the same,as far as I know.
2 From the DDPG the airplane can be dispatched under some conditions (day VMC,...) with only one IRS operative.
But ,I guess your question about difference between headings fits somewhere else.
7 Maybe it's night and I'm tired ,but Lem,where is the window heat off NNC?
4 The gearbox is placed on the 'outside' of the engine ,that's the reason for the particular shape of the 737 nacelle,and indeed the fire extinguisher does not reach the gearbox.