I doubt it - the bootloader is very different on iPads and I don’t think it would let you boot a different OS

Only if the hash function is designed well

For a launcher, I’ve been using Neo Launcher (which is on IzzyOnDroid). It’s not as feature full as Nova but it’s pretty similar in spirit and style

I’ve got a ZenFone 9 which is excellent and I think fits all of your criteria. There’s not many stock apps from what I remember, and they’re all easily removable (which I’ve done, you may need to do some ADB trickery). It also is pretty small, has excellent battery life and a headphone jack.

The only missing thing is that there’s no lineageOS support just yet, but there are some other ROMs available.

Yeah, my ZenFone 9 has been a great upgrade from my old Pixel 3a. I’d expect the ZenFone 10 to be slightly even better