I put together an OpenBSD guide on this topic. I haven't updated it but it still should work.
BareGUI for OpenBSD
Going forward, one concern is the future viability of OpenBox. It is still GTK2 based and the forked code shows no recent commits. Same can be said for Fluxbox and Blackbox.
There is space in the OpenSource ecosystem for a lightweight, stacking WM based on GTK4.