Get decent quality at least 4mp.
At least.
I've been playing with cameras/recorder. My kit came with 4x 5mp cameras and a recorder that will display from 9 cameras.
From a previous attempt to get something working, I bought a 1080p camera. The new recorder will talk to the 1080p camera, and display it next to a 5mp, so it's easy to see how horrid it is.
The recorder in my kit is spec'd for 4k, so silly me assumed it was supplied with 4k cameras (burnt again). I've just ordered one 4k camera to compare and hopefully number plates will be readable.
My 1080P is mounted above the workshop door and you can identify someone (you know) to about 6ft. Much beyond that, it's hard to tell if it's human or alien. It's not a camera to take seriously.
Depends if you just want a movement warning or if you need a pic that will stand up in court.
4/5mp is certainly min. spec, but consider 4k.