I’d not recommend Synology anymore, as they’re starting to implement vendor lock on their drives and NAS boxes. As in, you’ll have to use their drives for the Nas to work.

I believe that the only FS that absolutely need to be on the root partition are /etc and /var. The rest can be anywhere else with various degrees of tinkering. For /home to be moved, you should just need to edit your fstab (or your systemd mounts, depending on your distro).

I really love all the 5+ years old articles about why systemd sucks.
It’s not perfect but it’s so much better than the plethora of different init methods Linux used to have. Also managing sysv init scripts sucked really bad.
It’s lightweight, most of it is optional, it’s declarative, it makes managing your systems much easier and it just works.