Opening credits say there are 47,858 human survivors.
The voice inter-communications devices used on the "Galactica" are actually the TA-1/PT field telephone, as used by the military for decades.
When Commander Adama is listening to the pilots during their asteroid weapons training his "Listening Device" is actually an AM-7162 which is the Master Control Station for the AN/VIC-2, mechanized military vehicle intercom system. It also has a modified LS-685 loud speaker connected to it where Receiver/Transmitter #1 should connect which would also power this device. He turns the center knob to increase the volume; this is actually the switch to turn on the "Internal Accent" which activates a noise filter.