Have not looked through the setup steps of that link, but using FDE with luks and remote ssh unlock for years and have not had any problems.
Also, when you update the kernel you have to rebuild the initramfs with sudo update-initramfs -k all -u, or it won't be able to boot to the new kernel.
Shouldn't that be automatically handled by apt? I dont remember that i have setup a hook for that and i never rebuild my initramfs manually.