I usually do the expert install and don’t install a graphical environment in the first place. But your solution should be fine, too. I think you can show running services with systemctl
and then disable unneeded ones. For example systemctl disable gdm
but there shouldn’t be that much running on a plain Debian anyways.
For powersave I run powertop
in auto-tune mode as a systemd service. A description is here: https://wiki.archlinux.org/title/Powertop
Unfortunately, the Debian Wiki doesn’t seem to have a lot on laptop power saving. The Arch wiki has some more (random) info: https://wiki.archlinux.org/title/Power_management
I’d say do the powertop systemd service on startup, set the multiuser target or disable the login manager and that’s it.
Everything has pros and cons. I’ve seen 3 laptops (of my family) with batteries that looked like a baloon after several years. I’ve subsequently removed or replaced them. I’d definitely check on them every now and then. A UPS is nice. Burning down a house isn’t. I haven’t seen them catch on fire (yet), they supposedly have at least some protection. But definitely get them out of the laptop once they’re dead anyways or don’t look alright. Everyone is responsible to make that decision on their own. Take care.