What LEGO Power Function parts do I need to make an RC car?
Your assumptions appear to be mostly correct. Just for clarity, these are the minimum parts required:


A battery box
A motor for driving
A motor for steering (unless you want to try a steer-on-reverse single motor design)
An IR receiver (these can support two motors each)
An IR remote


Extension cables and/or lights are optional depending on the design of your vehicle.