Audio: Simple answer is 3.5mm jack to RCA cable running to Aux input of a headunit.
There are other solutions, but this is by far the simplest.
For the auto on/off, you have several options:
You can have the laptop turn on when it senses power.
You can have a unit like a Carnetix power supply or a dedicated startup/shutdown controller mimic a press of the power button.
There is a laptop auto-turn-on module made by a forum member.
You can be creative and use Wake on Ring or Wake on LAN if your laptop supports either.