I can answer a couple...
4 - answer NO. It's one or the other.
5 - It's a pain in the proverbial... the HHP changes the password of the camera and keeps it secret. In theory, when removing a camera, the HHP restores the original password which would give you access again. In practice it did this in oly one case out of 8 removed - the remaining 7 required a hard reset. If they are outside, near your roof, this can be one hell of a challenge !
6- from memory - YES.

Only other point - upgrading the hard drive... as cgh001 mentions, the 2TB supplied HDD fills up quickly. Camera configurations are stored on a chip, not the HDD, I am reliably told, so you can change/upgrade a drive without losing all your configs. Proof of pudding coming tomorrow as 10TB drive arriving

I just wrote a long explainer, pressed 'submit' and your server said 'timed out'. It's too late to repeat !

@joseph_1979 Thanks, Joseph. Unfortunately the instructions in this link (which I had found previously), bear little or no relation to what I am actually seeing on my app or computer. In the end I deleted the cameras and am now in the process of resetting each to factory settings. This is fine for my very recent cameras, but trying to find instructions for my older (4 years?) cameras seems impossible.

Does Reolink have an ARCHIVE page anywhere, perhaps ?

Anyone know how to remove Camera from home hub, and have it retain its original password ?
Thanks