I am guessing you have the electronics add on? I got rid of the electronics and just got a powered USB hub and get power from the 12v lighter on the passenger footwell. On mine the audio jack on the tablet used to go directly to the amp, now I use a AudioQuest Dragonfly usb audio stick for the output to the amp.
As far as a backup camera, your pretty screwed if you want it on the tablet. It is possible but options a limited and not great. I was able to get it to kinda work with an EasyCap USB 2.0 Capture Card and a typical backup camera and the app "USB Camera - Connect EasyCap or USB WebCam". But I threw all that out because by the time the tablet booted, the app loaded, the camera connected, and finally the video displayed I could have been where I wanted to go. Solution, I wanted a dash cam anyway, was to get a rearview mirror dash cam and back up camera in one, any 100-150 dollar one would be good, mine was a VanTop brand but they are all the same as far as I can tell. As far as steeringwheel control input, ugh. There is a way but it isn't easy. You need to take the resistive inputs and wire it up correctly to this, RcJoyCon CPJexc or CPJexr types should work, and connect that to the USB hub. It can be programed to receive resistive inputs like those from our steering wheel and be programed to give usb keyboard outputs. So you can have your volume up key work just like a USB keyboard with a volume control. Its a S.Korean board and has no documentation that I could find to help. I have two boards slightly different but haven't put in the effort to figure out how to get it to work, but it should.
Talking with Brainiac was while very polite, unproductive, they offer no solutions besides "others are able too so it is supported".
Audio
USB Power Hub
USB Power
USB Drive 70C temp
Mirror
Resistive input USB keyboard Out
There is a way to get around the steering wheel controls, simple get a Bluetooth device with a pause/play/next and mount it within reach their are a few battery power ones thy make for cars and bikes that should work well.
Bluetooth Buttons
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