I like to have a screen, even if i can not read the settings menus without my reading glasses, you will not be the first one dismissing some cameras as they appear large, but most dashcams are adequate small, if you go by volume of the housing the Viofo cameras are probably the same as any BV / TW camera
But you are right in that some cameras are more suites VS others in some cars, the wedge cameras often come off as just another sensor on the windscreen, the Barrel shaped cameras can be a better choice in other cases.
We all want out setup to be as stealthy as possible, i have a dotted area in front of my roof mounted mirror, so i can mount wedge cameras there so just the bottom 1/3 with the lens peek out below the dotted area, making for a very stealthy install.
Yes only relevant in parking mode, but we are still talking milliamps they use.
Yes thats no problem, if the camera have been hardwired into a fuse to enable parking mode, you just have to take out the piggy back fuse adapter and put the original fuse back in its place, and then of course remove the wires.
If you have a regular setup powered by the dashboard cigarette lighter socket, you just have to remove the wires.
The cameras them self can either be installed with a suction cup ( rare these days ) or with dual sided tape, they do stick on well with the tape and it can require a solvent to completely remove any trace of it being there.
You can probably switch cameras between the piggy back fuses, meaning use the same piggy back fuse adapters in the place they are, some modern cars can be a little fussy about what fuse to use, which can cause irregular behavior, but with the right fuses used it will most often work as indented.
Most hard wire kits today are the 3 wire kind, meaning there is a always on +12 V wire, and a ACC on +12 V wire, and then ground to connect, but the hard wire kits are not universal you will need to get a BV hard wire kit for a BV camera and a TW hard wire kit for a TW camera.
If you have / want to have 2 systems hard wired, you can do that of the same piggy back fuses, but as a hard wire kit only have 1 output and usually also only enough power for one camera, you will need to connect 2 hard wire kits to the 12 V piggy back fuses in your fuse box.
And this can just fine be different brands of hard wire kits / cameras, as you are just sharing on the 12 V side of things that will be alright, but if you have used a 5 A fuse for the dashcam, with 2 systems connected you might want to go up to a 7 A fuse,,,,,,, at least that should be on your mind.
On youtube you will find many videos on how to install a dashcam in a car ( regular power and hard wire ) in general this is the same in most cars in regard how to route wires and how plastic trim are removed from A pillars and so on.
It do not require intricate DIY skills to install a dashcam, but you do of course have to know how to treat DC power and not short + and - wires, beyond that you just need basic tools like a Phillips head screwdriver.
Me knowing my little car well after having put in and taken out dashcams for a decade, i can put in a new dual channel system in under a hour, and if it is not hard wire i can do that on a gravel road in between Mr. Johansens fields.
If it is hard wire i do need a soldering iron as thats how i like to put wires together VS using crimp connectors / tool or some screw together gizmo.