I prefer the approach of AntiX and MX Linux. Start from a clean live distro, mod it to your taste, master it to a new Live ISO. You can also start from a normal MX/antiX system and make a live ISO backup. You can also install those ISOs. Systemd is optional on MX and disabled by default. LOTS of live and remaster options on those systems. I find myself more on live than on installed systems now. It's basically like working with FS snapshots.
A similar distro with remaster tools based on Devuan is Refracta.
There's almost no circumstance I can imagine where giving up a solid usable well known OS sounds tempting to me. Getting Debian running on PogoPlugs and OpenWRT devices has been a repeated ordeal I'vd gladly traversed. Having a well behaved normal OS that meets many user's expectations (but has your special stuff regularly installed!) is divine.
I used to run Debian Live, and appreciated the tiny amount of shell hacking they have to layer persistent storage filesystem atop a ro filesystem- identical to how theres a ro container image then the mutable rw layer atop it... but a decade older!
I find that the pretense of running "live" is largely gone. It's basically become a meaningless difference of what medium you run on but I've been using the same scripts to create the necessary root OS & UEFI EFI filesystem (FAT32 with a magic partition-type, populated with the bootloader & config). often I spin up systems by just copying a btrfs snapshot & rsync'ing efi directory (and updating some partition uuid's, regenerate machine-id), then I have two systems. Live feels meaningless, non-distinct from regular to me.
All these attempts to treat things different & distinctly, to make special cases for ourself- oh we need a network/router oriented OS, we need a bare OS, we need a consumer OS, we need a NAS os- so rarely have I ever felt like these attempts to flee from the fold & venture out to special really have rewards. This behavior of making exceptions for your problem, talking yourself out of doing the easy normal base thing, seems so rarely to me to have rewards. Run Debian, run systemd, run normal well-known tools! Unless you're really certain getting off the base path really is essential, has huge specific merit.
That's why I like this effort. It allows customization & baking your own thing, but it's much more routine & regular & normal than so many "make your own OS" projects, where folks tend to be quite "back to the land" in motive. Let's make our own OS from sticks! Yeah! But no. You almost certainly should have an ok userland base in my view. Debian is a pretty great one.
If anyone wants to build with/atop Debian Live, I did a couple projects years ago where I wrote wrappers that might still be good starting points:
* LilDeb, a USB multi-tool designed for 256MB (like when you couldn't find a Linux box, but you could find a Windows PC), with careful separation between read-only OS, ephemeral data, and persistent data. One shell script builds the entire thing, including the various config files. https://www.neilvandyke.org/lildeb/
* Rackout, start to a living room media appliance project that was going to provide some examples for my (abandoned) Racket book. If you happen to want to use Racket to do things like repartition a disk or build a distro image, some of the libraries I wrote might come in handy. https://www.neilvandyke.org/rackout/
How do you maintain this as new base releases are made?
Ie: Do you just manually reapply your changes every time? Or just do in-place upgrade and then snapshot that?
Personally, by the second time I did this, I'd be writing a script. Then I'd want to script the running of the script.. and before you know it you end up with a framework..
A similar distro with remaster tools based on Devuan is Refracta.
There used to be the Debian Live project but it looks obsolete. EDIT: sorry I misread the bug reports, it is OK https://live-team.pages.debian.net/live-manual/html/live-man...