May I say to you all - thank you!
I undertook the mini-project of migrating MSR from SD card to SSD. Full transparency, I'm not a Linux guy in any way/shape/form so there was a good deal of feeling my way thru the dark. Once I got it moved and running (honestly, on the first try!) I wanted the next logical step of start/restart at boot. Was really fumbling until I found this thread - it was better than any tutorial I'd been using.
Success is mine: on the SSD and with everything starting at boot like desired.
Thanks @Matteburk for making mistakes similar to mine and to @toggledbits for his INFINITE patience and guidance. (The app -p thing was actually a question I had after seeing an earlier screenshot in the thread and having removed it only to meet failure nose-to-nose.)