Can’t have grub problems if you don’t have grub. The howto is great, I’ve converted a few machines using it without any (subsequent bootloader-related) issues.
Only to activate the new kernel! You can just leave the current one running with minimal issues, even less if you have something like KernelCare live patching security bugs
sudo pacman -Syu is equivalent to sudo apt-get update && sudo apt-get upgrade, you'd want to run it about once a day to ensure you have all current updates. Pamac should allow you to update everything from a GUI, so you don't have to worry about that.
Is there a safe way to do uodates automatically? I could store my password in plaintext and thats barbaric but it still doesnt fix the problem that packages and dependecies can break during updtaes without user input if im right. Tho i guess you could write a script that automatically looks for updates and notifies the user.
The task is objectively unsafe. Both live updates are unsafe and require intervention but also Arch does not guarantee updates require no manual tasks.