TS10 and 7862 essentially uses the same chip. difference is on the motherboard design and software customization. TS10 will run a single channel DSP 48band while 7862 runs 2 channel dsp 16 band for each channel. Amp output for TS10 is superior compared to 7862 but TS10 doesn't hold a candle if you're talking about SQ or audio clarity. TS10 is just vanila or android kosong slapped with manufacturer's custom add on. Ecosystem is locked, they will hinder users from modifying the internal. 7862 is open, UI and software is yards more polished. The essential items are displayed outside only technical configuration settings are placed in the engineering mode. unlike TS10 there's 2 hidden engineering mode which is very confusing.

4 is bare minimum which can ge you through for another 1 to 2 years before its going to run out of breath. software developers now are designing apps to work with minimum 6gb android machines, unless you're using google's official product where optimization is done from the proprietary google Android OS itself. e.g Pixel & chrome.
solely depends on your dashcam whether it can support streaming on the fly. when you stream your dash cam will need to work 2-3x harder. heat can shorten the life of your dashcam.

if i were u, i would keep both independent. because you will get better quality if using independent dashcam, and if ur headunit got problem etc, at least ur dashcam will work.
and if you just need to see the view, why not install the dashcam apps and stream from there ?, but normally it will stop recording.  is there any reason why u want to view the dashcam on ur headunit , minus correcting the view angle ?

on headunit, if u need to see the view like the back, then install the reverse cam or other aux cam connect to ur headunit, can install both front and rear.. this way u can always view the cam while driving.

for reverse/parking etc, you can install 360 camera, but need upgrade ur headunit that support this.

Still got newer Unisoc? Isnt the UIS7862 is latest one already?