Preparation
Some things to bear in mind before continuing,
What made this much easier and faster was having the original Toyota double DIN head unit. I pulled this out and completely gutted the electronics from the entire enclosure, then repurposed it for this entire project. This meant when it came to mounting the unit back in the car, it just fit straight in, perfectly!
Originally I cut the factory wiring harness out and soldered everything directly on, I later changed my mind on this to allow the unit to be easily removed for future upgrades or repairs etc. I do plan to get the steering wheel remote controls working in the future, so figured I would be taking it out again at some stage. I would also suggest keeping the wires long enough that you can place the unit on the seat or the dash while still plugged in for testing purposes.
This unit requires internet for almost all functionality. This can be achieved by either a wireless tether from a phone, or in my case using a USB LTE stick, but remember this is going to require a data plan to operate.
I also strongly suggest flashing the SD card and configuring all hardware prior to installation. There is quite a bit of modifications that will most likely be required for the OS for some of the hardware to function. This is much easier when things are on the test bench and not installed in tight places. Then when everything is working and tested, go ahead and install as neatly as you can.
Wiring Diagrams
Below are the wiring diagrams for the power and audio.
