Newbie with basic questions

To add to what was said above:

The PSD is lubed with ATF fluid (not sure what type).

The only belt is the water pump - for the ICE. There's a second water pump for the ICE for heater purposes. There's also an electric water pump for the inverter cooling system.

Air filter is every 15-30k miles depending on use.

To directly address #1:

In the classic prius, there was an electric motor straight on the steering rack providing assist. In the '04 and later (version 2.0), the motor was moved up to the steering colum. If you have the car completely quiet, you'll note that if you turn the wheel, you'll hear a slight whirring noise. If you're adventureous, you can take off the dash panel behind the steering wheel and see the motor assembly.

The motor provides assist (or resistance in VSC cases) based on torque sensors (which detect slight rotation of the steering wheel vs. the steering column shaft itself), and then via a motor connected with a worm gear, assist is provided. In cars with VSC, a light-wheel type sensor is also included to detect how quickly the wheel is turning.