There is a Nova launcher beta: https://novalauncher.com/beta

Yes, you can install on one machine, move the drive to a different machine, and it should mostly just work (unless they are different architectures and the packages aren't compatible). I've recently moved an old Arch install into a basically new computer and after changing the microcode it just works fine.

Yeah I think so. There are some optimisations that can be done to improve things, but at the end of the day it's running off a slow USB drive

I've just got Arch Linux installed on a USB drive. I set it up so it works with both UEFI and legacy BIOS boot. It works great - I can install whatever tools I need on it, I can even use it as a little portable Linux drive if I need that. I've also used it to install Arch on a number of my computers.

The only issue is that the USB drive is pretty slow, so it's not the best experience using it

These look awesome! I'm curious what your favourite switches are out of the bunch? I'm also interested in a comparison between the Boba U4T vs MMD princess, if you have any thoughts to share!

Looks great! I recently put together a similar build with the same mobo/CPU, and it works very well. Just note that I had to do some fiddling in bios options to get it to shutdown/sleep properly, but all is good now

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

Do you have any aircon companies that you do recommend?

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