Anonymous
To make the answer short:
LightDM is lighter then many and heavier then some — it’s a middleweight application.
Same applies for Xfce/Xfwm — too litle for DE, too much for WM — middleweight.
The combination of Xfce & LightDM prooved to be robust and works well.
There is no reason why you shouldn’t be able to use Xfce with Slim just as well.
Obvious would be somewhat less functionality at the Log In screen (F1).
Devuan and Devuan based Distros usually use Slim as default.
Installing Xfce and LightDM on antiX is a nonsense. You could simply use MX instead.