Now, for wallpaper and desktop icons you need pcman to be running in daemon mode, but if you only need wallpaper-ing you may use feh.
I prefer phototonic as image viewer and wallpaper setter (via feh or pcman).
pcman doesn't need gtk really, but lxqt currently seems to need for some things, but then I've removed some time ago lxqt (and feel guilt –a bit!).
So in my system if I try to install libfm-git pacman just warns me to replace libfm and libfm-extra with libfm-git, i.e. no appearent issue here.
I don't know a replacement for gnome-keyring and yes, don't save passwords.