I don't mean to be negative, but this sounds financially silly. At least in Australia.
The parts required will cost more than a commercially available 'reversing cam'.
For example, an RPi3b from an official reseller will set me back $70, hardware to power the Pi and shutdown gracefully, another $20 or so, monitor $30-$80 from China, Raspberry Pi camera $30, wiring etc, depends on how much is needed, solder, mounting equipment, etc..
We're already at more than $150 (and thats excluding shipping and electricity costs)
On the other hand, I can buy a commercially available reversing camera that installs with all necessary acessories included, for $60.
Sorry if this is not a very useful post, but I really do wonder what purpose such projects as these serve.
Stop plugging your fan directly into the GPIO 5v