Make sure that your Fallout4>Data>F4SE folder only has 1 plugins folder. I ended up with two, Plugins, and plugins, somehow.
If you have that, move everything in Plugins, to plugins, and delete Plugins.
Library Addons goes into plugins, Plugin Preloader goes into /Fallout4, where the Fallout4.exe and f4se_loader.exe files are.
I think I ended up with two plugin folders from just dragging the folders into data from the archives of the mods, instead of moving the files inside of them.
This assumes you are installing the mods manually and not with mo2… but even with mo2 its better to check than be sorry, I guess.