I first set up this Arch installation with Xfce and the xdm-archlinux display manager. Decided later to add LXDE; and, I switched display managers, going with LightDM, which is nice for choosing from different desktop environments/window managers at login.
# pacman -S lightdm lightdm-gtk-greeter
# systemctl -f enable lightdm.service
For info and instructions about display managers for Arch, man pages and the documentation at the Arch wiki prove essential.
To get a screenshot of the greeter screen, first I had to add xorg-server-xephyr:
# pacman -S xorg-server-xephyr
Then I used dm-tool to run start a nested display of the greeter screen, and took a screenshot of that:
$ dm-tool add-nested-seat --fullscreen
Alt-F4 gets you back to the desktop. Also, see dm-tool --help.
In Arch's default LXDE, I wasn't able to change the number of desktops/workspaces. The thing to note here is that not all options for configuring Openbox are available with the lxappearance-obconf plugin (and that obconf is needed to change the number of desktops in LXDE). So:
# pacman -S obconf
A clean look at how I've got the desktop set up at the moment: