From your questions I'm not sure as though you understand the purpose of this light? It is to run ambers that you turn on via the aux switches so that people behind you can see your truck when driving off road. If this is not what you are buying it for then don't buy it.
1 - Not really imo as you have to run the wiring harness along the cab and wire the amber lights up inside the fuse box area. Yes the three leds and cargo have plugs (which is appreciated), but if you buy the harness to have the center light come on with reverse you have to tap into a wire in the BCM connector in the fuse area as well.
2/3 - as mentioned the three LEDs light up when braking
4 - Most people wire it with white in the center (which would come on with doors open) and ambers on the outside. You could do white ones on the outside if you wanted to blind the neighborhood while getting your mail.