Today I found a PEBKAC error was causing part of my issues -- on one laptop and the netbook which have SSDs, I had previously mounted /var/log on a tmpfs, so of course it was not possible for anything to be persistent including the systemd journal. (headslap here) By changing that setup, and then making the /var/log/journal directory, and the next item below, they're working correctly.
Then make the directory for /var/log/journal as devil says, and after reboot it is working correctly on the Dell laptop I posted above and my other computers. With these two things corrected, it looks like I can set the journal to be persistent at /var/log/journal on all my systems, so that's a closed issue.
HOWEVER, I believe we still need to develop correct guidance for taking the system to the level formerly known as "init 3" (no X server running) for d-u. Today I discovered that when you use:
systemctl isolate multiuser.target
it also kills the ssh service, so that is no good for remote administration. I'll have to wait for one more knowledgeable to figure out a correct procedure for d-u on a systemd system.