I'm just embarking on this as well. My current thinking is to mount the tablet magnetically on this thing.

Bought this dongle.

Installed the app on a 2015 Fire 7 tablet I had laying around. I may deregister the tablet from my Amazon account just to guard against the app-from-random-website buying Amazon stuff or Audible books.

Seems to work fine sitting here on my dining room table, but the first OTG/Charging adapter I bought doesn't support OTG and charging simultaneously, so that's going back and I'm going to try this or this to see which one wins.

Both the phone and the tablet do show up as "Charging" when this first adapter is in "Charging" mode, though, so that isn't something I'm worried about yet. Worst case I suppose I use something like this to get power to the phone individually.

I'm planning to mount the Carlink widget on the back of the tablet with some command adhesive or what have you, then I can pop it off and toss it in the glovebox when parking.

I haven't yet tested the Bluetooth connection from the Fire to the car, but worst case I use an aux cable.

So far I'm pretty excited. I just bought a 2014 Leaf and am missing CarPlay from the car I replaced. When I bought it I started looking into that $500 contraption that hooks into the reverse camera, then started thinking about what would be involved in making a minimal "CarPlay" screen maybe out of an RPi touch screen. Then happened upon this widget.

The fallback plan is to buy a cheap carplay-compatible head unit and disassemble it so I can mount the screen on a stick and put the head unit itself under the seat [this Leaf has the "fancy" stereo that's tied into the climate control and such].