Where does the initial energy source come from?

The electric motor gets the electricity to turn the friction wheel from the energy cell it is plugged into. The energy cell gets recharged by the steam generator. The steam generator gets the steam from the boiler. The friction boiler will make more steam than you ever need.
How long will the wood last?

This depends on the size of the heater.
Using the heater shown in the video, the wood will last about 3 days.