I came to the same conclusion when I built my NAS. Just Nix for the system, zfs for raid and docker compose for any service I might want to run. https://www.splitbrain.org/blog/2025-08/03-diy_nas_on_nixos
I've seen the quadlet-nix project but don't get what additional it gets me.
Thanks for saving me probably some hours...
EDIT: I'm also coming from an old Synology NAS from the ~2015 era.