I have a very large cab, so I use 3 nozzles, but I believe most people run just one nozzle in the dash area. I use two 10lb bottles.
My internal three are driver (from the side at a 45° angle to hit me from feet to neck), one to spray the floor in case oil or fuel puddles there, and a similiar one for the roof in case I land upside down, it will do the same as the floor unit. It's AFFF (Coldfire).
For the engine, I run 3 Halon, left + right headers, and a smaller direct injection nozzle into the intake to kill the engine in case of a runaway.
That is probably overkill for a car though, and the intake nozzle is diesel-specific. Diesels don't always shut down when you kill the power.