The three wire kit unlocks parking mode with battery monitoring so your car battery won't die. I think the camera should still run off your current kit so it's worth a try. Worst case, you can order the 3 wire kit later.
My advice would be to also put in a new SD card. Not sure how many years you've had the V2, but I always get a fresh card just to ensure that it won't fail on me. Something like the 64gb high endurance should be good for the A119 Duo.
I also recommend getting a dashcam optimized SD card, such as the Sandisk High Endurance or Samsung Endurance Model. Dashcams place a lot of read/write cycles, so a regular SD card will fail more quickly. Fortunately, they are usually on sale and very affordable. Definitely recommend that over the Ultra
That's a tough situation. Does your rear shade go all the way up or does it leave a small gap near the top like in the gif you posted?
Also, are you absolutely settled on a rear dashcam? 90% of accident situations will be captured by the front, and even when someone rear ends you, a front dash cam can show that you didn't make any dangerous/illegal maneuvers. If you can show that, it means you are not at fault.
If you're okay with a single channel and it's in your price range, go with the single channel DR750s. Alternatively, for much cheaper and essentially the same quality, check out the Vantrue T2. I have read really good things about that camera.
One other thing that I will add that if you get a camera that doesn't include an SD card is to make sure to get a dashcam optimized SD card, such as the Sandisk High Endurance. Dashcam place a lot of read/write cycles, so a regular SD card will fail more quickly. Fortunately, they are usually on sale and pretty cheap!
Make sure you get a good memory card if you're buying a dashcam today. The Sandisk High Endurance is its normal price of 64GB for $29 on Amazon but that's the best high endurance memory card price I've seen today nonetheless.
Having a CPL filter actually reduces glare on daytime videos but has a slight negative effect on nighttime recording generally. So not having one will actually improve it.
I'd go for a 64 gb card, and spefically a high endurance once like the Sandisk one. They are only a few bucks more than normal ones but apparently better for the cycles that video monitoring systems place on the cards.
As for buying on Amazon vs Viofo, i'd go with the one that's cheaper or has better shipping options. Also, Amazon has easy returns if something happens. Not sure about the Viofo store.