I don’t recommend it, it is the only supported OS for a Supervised install now.
It is as customized and somewhat bloated version of Debian specifically for the Pi, but contains a lot that is not required or needed to run HA Supervised.
As per my first comment, Debian 10 is the only supported OS, so if you use a variant, like Raspberry Pi OS, it may cease to work at any time due to changes being made in HA, like preventing updates which has been widely discussed over the past months.
Not going to happen.
There is none, HA Supervised runs very well on a Pi 4 with Debian, if anything, it boots faster being that the OS is less bloated.
No idea, but this is not really needed. The installation time for Debian on a Pi would be about the same amount of time it takes to restore an image. I can set up a new install following the Debian/Pi guide, with HA up and running in 20mins.
You’d be best off installing the Google Drive Backup add-on and if you face a corrupted drive, perform a fresh install and restore your backup. Very easy.