[banks99]

Heres a relevant review from the system you linked. Its not worth it IMO to retrofit these systems:

We followed the installation instructions to the T. Even the vehicle in the diagrams was almost exactly like the car we were installing it to (2016 Honda CR-V). Installation was easy and straight forward, except for connecting to the reverse wire of the simply because the harness supplied would not reach. Once installed we placed to oil barrels where one would suspect a car in your blind spot would be, and sure enough, the warning would illuminate and beep if you tried to use your turn signal. Time for a road test.... sadly, that's when everything went wrong. The system would pick up EVERYTHING as being in the blind spot, but when an actual car was in the blind spot, it wouldn't even activate. We checked the instructions, checked and measured out the positions of the sensors. The bumper is a flimsy plastic so we didn't suspect it was causing issues with the sensors... we couldn't figure it out, so we had to tear it all back out of the car, pack it up and ship it back. We were excited to try it, but it wasn't ready for the real world yet.

You could just install a second dedicated rear view/side view camera with a separate screen if this is a major concern for you: For example:

Cameras

 

[banks99]

That was just an example to illustrate what type of system I'm asking about. i know a $100 system won't give me 3 great features. i suspect $500 or so may be a price something good could exist?
the problem still will be to calibrate and fine tune the sensors (and the processing of signals). and for each car those get installed, the sensors will be in a different angle. So maybe this is not going to be a successful mission of mine.... A system that is annoying all the time won't enhance safety.

Not sure I want to look at complex camera systems. they will not work well under adverse conditions like night and rain. i find it funny that Tesla goes away from radar and solely trusts cameras because "humans also drive with vision only". Yeah, and humans suck at night, fog and rain driving.....

I was hoping to just replace the camera and use the regular OEM screen. Maybe adding a new stereo with screen could help if that has a good camera option. But where would I install that camera? and would that also be activated by gear in reverse? Sounds like i would need a lot of wiring harnesses specific to my car. i was hoping there is a place that sells all those specific to my car. I know Crutchfield has all that for stereos for specific cars. So maybe there also is a place for cameras or radar sensor?

Yes, you could install a new reverse camera and headunit. Wiring is not very complicated and there are many tutorials on line. Most new cameras have licence plate brackets that you attach the camera to. You would not be able to wire this to your I-mid screen. You would simply have two rear view cameras

 

[banks99]

I think installing a second camera may be an option. I looked a bit at Crutchfield and came across these: please advise if the general idea is good:
Boyo License plate camera and blind spot detection it looks like i need some sort of display unit or mirror with display. it says it has a 0.1 Lux rating and 976x592 resolution. 175° angle. Is that good for night? Looks like low resolution since it is way below HD. it may be above Honda, but that is an easy achievement . I don't think it uses radar, so I'm not sure how blind spot detection works.

Several mirrors with display. Some with camera, some without (could be combined with above license plate camera?) I'm not sure if it is legal to give up the real mirror, and if the camera isn't great, i would not have the mirror. So I'm not sure i like to have the tiny mirror display

Several display units. Some with, some without camera. I think that would give me the best way to see the rear camera (large, and i still have the analog mirror). A long time i was looking into this for other reason. So this isn't the worst upgrade.

Some questions:

• is running the wire from back to front a reasonable task while looking good? Does the rear camera get power from whatever front unit I use?
• what minimum data specs should i aim for to get a significant improvement (resolution, lux etc.)
• Besides Crutchfield, what are good places or brands to look at? I want a reasonable price, but something I'm happy with and enhances safety.

Edit: I found the Boyo manual and it says it uses microwave radar

I am not an expert on resolution, lux, etc for backup cameras so I cannot address that question. You should look at reviews/pictures once you have narrowed 2 or 3 down.

Crutchfield is great for exploring vehicle specific options and have great customer service if you have questions. Rear cameras generally get power from either the head unit or the reverse light. Your best bet may be to see if a best buy near you does installation. They have a decent selection of backup cameras and headunits that are reasonably priced. I would avoid the mirrors with displays if your issue is with visibility/quality.

I think the bestbuy purchase and install may be the best option for you.