Working Builds

NEEDS REFORMATTING For the Pi, I'm using a 4b with 8GBs of RAM, it isn't bad but if you could find something a bit more powerful it wouldn't hurt.Display

I have this display: https://thepihut.com/products/8-ips-hdmi-capacitive-touch-display (Waveshare 8" HDMI).
    Size: good for a car, less bezel than the Rpi official display but not much bigger in overall size.
    Brightness: Dim enough for night driving, could be brighter in direct sunlight, but still visible for me (must set maps to light mode)
    Brightness control: Technically possible from the Pi, but I have not gotten it working consistently enough, so I use the included controller board.
    Connections: Fullsize HDMI, 2x USB-C: 1 for touch, 1 for power (I have found it can be powered from the Pi using the touch port only, but your mileage may vary).

I was originally using the RPi Official 7 inch display, but I got it used from marketplace, and it was damaged and eventually died. 
    Size: A bit small in my opinion, bezels are quite large
    Brightness:  Fine for night driving, a bit dim in sunlight.
    Brightness control: Can be controlled directly from the Pi.  I even had a script to auto-dim it using a brightness sensor I bought.
    Connections:  I don't remember fully, but I think it had the Pi cable for display, and used pins for power and touch.

Sound

I am using the onboard audio for audio out, and a generic USB card for mic-in.  In my testing, I found that if you want to take phone calls, you need the audio-out and audio-in to be plugged into separate controllers (eg: soundcard for mic, Pi for aux-out).  I put this in the wiki page I created for getting hands free calling working.
I also purchased an external bluetooth adapter as I thought it was needed for hands free calling, but others have gotten it working with the internal BT.

Power

To power the Pi, I am using a PiSugar (specifically PiSugar3) as recommended by
[@tmcnulty](https://opendsh.slack.com/team/U04102XMHSN)
.  This gives you a nice battery backup which is great for me because my car temporarily cuts power to the radio when I start it.  Its literally 3 seconds at most, but that would previously cause the Pi to restart and was especially annoying if I ever stalled.  Regardless of what you use, you will need an output that provides 5V 3AMP consistently.  NOTE: If you get something like this and mount it directly to the Pi (which I found was the only way to get it working fully) it will prevent you from mounting directly to the back of the Waveshare display, so you'll need to get cables to connect it. I think you could still use the official Pi display mounts as the wires have a bit of slack.
To power the PiSugar, I have this 12v > 5v converter: https://www.amazon.co.uk/Converter-Reduced-Voltage-Regulator-Interface/dp/B08VHZJ3C8.  I can't vouch for the quality of anything on amazon, but that is the one I ordered and it is working so far.  To connect it to the PiSugar, I just cut a USB A > C cable and soldered the 5v and GND.
If you plan to connect your phone to the Pi, you may find it doesn't charge your phone.  Some people have reported that it holds the charge for them, I found my phone actually drains very slowly.  To fix this, I bought this powered USB hub to solve that: https://www.amazon.co.uk/SABRENT-Powered-Splitter-Indicators-HB-UMP3/dp/B00TPMEOYM/.  You will need a separate power supply capable of 5V, 2.5AMPs.  I cannot recommend this hub though, I have had constant issues getting it to charge my device consistently.  I am pretty sure it is caused by the hub power being cut and then restored when the car starts, but I cannot say for sure and would not feel comfortable telling someone to buy one.
If your power source is always on (my radio lines were), you will want a relay to cut power when the car is off.  I got this one with a delay, but I don't use the delay: https://www.amazon.co.uk/Delay-Timer-Relay-Self-locking-Switch/dp/B07SR4BX95/.  The DC+ - are connected to the radio power and then X1 is connected to ACC,  I then jumped DC+ to COM and connected the 12v > 5v converter to NO (normally open, meaning normally not live).  You use the set button to switch the function to be controlled by X1.

Other

It looks like your car has steering wheel controls, if you want to keep using those you'll want to research how they work.  In my case, they were "resistive" buttons.  If they are resistive, you will need a device that can read analog signal.  The Pi CANNOT do this on its own, but I believe Arduinos can.  In my case, I wanted to use the Pi for everything, so I got an MCP3008 chip which converts analog signal to digital.  I can't remember where I bought mine, sorry.
If you plan to use the Android Auto wirelessly, note that there is currently an issue where the alerts from Waze, Maps, etc get kind of stuck/delayed.  Doesn't effect music or phone calls.
If you are stupid like me, its probably a good idea to disconnect your battery when connecting everything.  I blew my ROOM fuse twice which caused a lot of other fun issues.