You need to know how much you're willing to spend on dashcam.
For 2 & 3, you can look for Korean dashcam as they are they best for dual dashcam and parking mode. But not cheap.
Dual dashcam from China cannot compare with Korean dashcam at the moment...
I've currently reviewed the mini0807 and the parking mode is working nicely and it's plugged to the OBDII port instead using a hardwire kit.
You can check my profile of the dashcams reviewed in LYN...
Another thing, most local shops are selling China dashcams and you can get them online like taobao, aliexpress, gearbest and banggood for way way cheaper.
Korean dashcam is very rare unless you look for them in JB or SG.
Taiwan dashcam like Transcend, Papago or Garmin, need to research a bit as their price is not cheap. Some are good.
Branded dashcam like Philips or Blaupunkt is expensive and you can get better specs dashcam from China for the same price.