It use to be possible to go back to sysvinit and purge systemd from Debian - for example - although I have no idea if this will bork your system
Requires some configuration of apt as well. I think the main issue you will have is the "the following command removes packages that depend on systemd itself or things like libpam-systemd!" warning in that method. You could end up not being able to use a lot of the Debian packages.
I tried that once and actually fully borked the system. I think I'll wait until anticapitalista and friends make possible to live in all the three Debian flavors safely without systemd. This is a wild bet, but I suspect they'll be switching to Devuan if it finally makes it though. I guess the way to go for now is keeping the system as simple and slim as possible to manage to keep systemd off. Too many packages depend on systemd now.
Not any safe way that I know of Snap. The surest way would be a debian base install and then remove systemd and replace with sysvinit and then make it what you wanted. That seems a boatload of work
Yes, it is a damn lot of work. Perhaps. as i said above, it would be smarter to wait for antiX to get there and using the antiX base instead of the Debian Net installer (which is similar but with antiX scripts on board and sysvinit instead of systemd) and build a Vsido-like (or whatever) on top of it. I already built a Vsido-like on top of PCLinuxOS lxde stripping it down to quite bare bones and then adding the Vsido like stuff. It ended up great, though PCLOS doesn't have the huge Debian's package base. Many things have to be installed from rpms or compiled from source. But the result it's great in the end. You keep using apt as a package manager and running on sysvinit. The login managers are restricted to just three: gdm, which I still have and hate, KDM and XDM. I think I'll go without any.
It worths the experiment. The VastOne's recipe to put a system together is just great on top of any system. Next step is a Vsido-like on both Void and Arch.
All this is due to my decision to jump away the systemd boat for once. I want to replace my current main system: SolydK (On Jessie testing when I switched to it and now on Jessie stable), for anything without a DE and systemd. It will be fluxbox and still don't know the system underneath. My first intention was replacing it for Vsido within the next months (too lazy for a full switch), but now it doesn't fit. I'm doing a lot of tests and different installs. That's why I'd like to build a Vsido-like on top of systemd-free Debian. If not possible, then going anywhere else. I'd like to keep going on Debian, but don't know if this is viable anymore.
PS, I haven't managed to make pclos vsido-like running as light as the real vsido yet. Vsido64 runs on ~100 MB of RAM at idle after a fresh boot. pclos is still iddling @ ~170 MB. Gotta sort this out.