If you already have a ZFS pool, I'd probably personally just throw on zfsbootmenu and a ZFS-root Alpine install. But, this is cooler and does have advantages:)
To log in and administer it? There's even an example; search for "extlinux --once". (There are other options, like a web UI or non-root SSH, but that's the obvious thing. Also if you want to advocate non-root I'm going to want to hear a threat model.)