There is more to determining which focal length lens to purchase than simply picking some random focal lengths to try. Each M12 lens is formatted to match a camera sensor of particular size. While you can use a lens designed for a larger sensor than you may have in your camera the result will be a FOV that appears as if you have installed a longer focal length lens than you actually have. Many dash cams and actions cameras use a 1/3" sensor while a great many aftermarket M12 lenses on the market are optimized for CCTV cameras that have 1/2.5" or 1/2.7" sensors. The inverse also applies. If the lens throws an image circle too small for the sensor you mount it on you will get vignetting.
There are other important considerations in choosing an aftermarket lens for a DIY project like this. Not all M12 lenses are the same. The lens you choose must be able to fit and function with your particular camera's lens barrel, so it requires the proper thread depth and the optical characteristics to match. This means that the lens you purchase must have a compatible BFL (Back Focal Length) and allow for the MBF (Minimum Back Focus) distance from the sensor. So, in some cases you could end up with a lens than can't be screwed in far enough to focus or you could have a lens that you end up screwing in so far attempting to focus it that you could jam it up against the sensor, thus damaging it. For related reasons, depending upon the lens you might also need to know other specs like the FFD (Flange Focal Distance), for instance. (varifocals have a flange) Of course, you'll also want to determine which aperture you want in your new lens.
Again,...... if you take the time to read and explore the threads you were referred to, you will learn all about this.
I think you are going about this backwards. To quote from
your earlier post in this thread,
"Maybe I'm delving into this project to fast. I'm still trying to find a unit to use here." I would tend to agree. I believe you will be better off first deciding on which camera you wish to modify and only
then begin to explore which lens or lenses would work best for your goals and be most appropriate for the camera you've purchased for the project.