You might not even need something like feh if you just have wget place the images in a folder the computers wallpaper slideshow function points to.
Also see below for some points on getting started.
I would love to see lemmy.ml(and other instances) grow. One of the things I actually I personally would really love is having a site layout option that closely mimicks old,reddits.com layout. I suspect this may also help the site grow given the that many long time reddit users really dislike the new design it may give them a solid push to check out lemmy.