I’ve always been attracted to a “text-only” Linux workstation, or minimal, tiling window manager like i3wm.
What I’m not sure about, and this is perhaps a basic Linux question, is how to
I use I3 and love it. It’s been a while, but I believe you only need to “apt install i3”. After that, the i3 option should show up on the login screen as a wm option after login. It took quite some time for me to figure out how to configure the system for gestures and natural scrolling on the librem 15, but by asking a bunch of dumb questions here, I got everything figured out. Many of the differences come from the default gnome environment being wayland and i3 using xorg.
Speaking of wayland, I wonder if anyone can comment on running sway (an i3 workalike for wayland) on PureOS. I notice the sway packages are not available in amber at the moment. I’m not sure I’m comfortable moving my main work laptop to byzantium just to try switching to sway. Is it sway a reasonable option on amber or should I just keep waiting?
I’m a long(ish) term i3 user and when I switched to wayland I’ve also switched to sway (i3 clone for wayland). By coincidence sway is also home base for wlroots which is used by purism for their phosh window manager (on librem5 phone).
What I use when I switched to sway is
if [ "x$WAYLAND_DISPLAY" = "x" -a $(tty) = "/dev/tty1" ]
then
export QT_QPA_PLATFORM=wayland
export SDL_VIDEODRIVER=wayland
#export MOZ_ENABLE_WAYLAND=1
export GTK_THEME=Adwaita:dark
/usr/bin/gnome-keyring-daemon -sd
exec sway
fi
mozilla is commented out because… don’t remember, i think my internet banking was not working properly in native wayland mode, may need to try again.
You’re right, of course: I just installed i3 from the package manager. I had to do a search, because I assumed it was called i3wm. 
Found this thread in which you commented, too. Will give it a read.
I’m still looking into the basics of “how do I turn this laptop text-only?” (i.e. don’t boot into the desktop environment…)
To (perhaps) answer my own question: Looks like PureOS has systemd, and so the way to tell the system to boot in non-graphical mode is^1:
sudo systemctl set-default multi-user.target
(as opposed to the current default of graphical.target)
Tested: this does, indeed work. Laptop boots to text-only login prompt.
Observation: the systemctl command above just sets a symlink in /lib/systemd/system/, and, if you look in that directory, there are all sorts of interesting .target files in there, including symlinks for the various runlevels. I don’t know enough about using systemd to grok the details, but I reckon you could do other interesting things with this.
Any alternatives, or considerations I’m missing, do let me know. 
yes you can, eg. you can create services for sleep target and have some tasks to be done before entering and after leaving the sleep state. Also you have session (not system) -level services and targets so you can add some services to start in your session or seat either explicitly (as pre-started service) or on-demand (as socket activated service) - eg. those which are usually started by DM/WM
$ systemctl --user list-units '*.service'
UNIT LOAD ACTIVE SUB DESCRIPTION
at-spi-dbus-bus.service loaded active running Accessibility services bus
dbus.service loaded active running D-Bus User Message Bus
evolution-addressbook-factory.service loaded active running Evolution address book service
evolution-calendar-factory.service loaded active running Evolution calendar service
evolution-source-registry.service loaded active running Evolution source registry
gvfs-daemon.service loaded active running Virtual filesystem service
gvfs-metadata.service loaded active running Virtual filesystem metadata service
pulseaudio.service loaded active running Sound Service
$ systemctl --user list-units '*.socket'
UNIT LOAD ACTIVE SUB DESCRIPTION
dbus.socket loaded active running D-Bus User Message Bus Socket
dirmngr.socket loaded active listening GnuPG network certificate management daemon
gpg-agent-browser.socket loaded active listening GnuPG cryptographic agent and passphrase cache (access for web browsers)
gpg-agent-extra.socket loaded active listening GnuPG cryptographic agent and passphrase cache (restricted)
gpg-agent-ssh.socket loaded active listening GnuPG cryptographic agent (ssh-agent emulation)
gpg-agent.socket loaded active listening GnuPG cryptographic agent and passphrase cache
p11-kit-server.socket loaded active listening p11-kit server
pulseaudio.socket loaded active running Sound System
user-level config is at ~/.config/systemd/user/
$ ls -1 .config/systemd/user/
default.target.wants
hcisleep@hci0.service
pasleep.service
sleep.target.wants
sockets.target.wants