I have been playing with rasplex the past few days since I have a synology NAS that I just installed the Plex media server app on. On the background image, i would not change it since it loads in a picutre based on the movie/TVshow you have brought up. for TV shows it will download the theme sound for the show and place it in the following directory /storage/.plexht/userdata/ThemeMusicCache I have downloaded 3 songs and the largest one was 909Kb. All the thumbnail images get downloaded to /storage/.plexht/userdata/Thumbnails ive got about 2.5 TB of movies and TVshows and my thumbnails folder comes out to 86,400Kb. So it does download some contect to the image. I do like the interface in RasPlex better than the PleXBMC addon for openelec but unless you can add more programs/addons to RasPlex I probably dont see myself using it unless it is in a triple boot system where I have openelec to stream and the RasPlex to view my home content. Granted I am working with 64Gb samsung EVO micro SDS card so haveing a dedicated 1 to 2GB partion for RasPlex doesnt bother me to badly.

Thats my limited experince with Rasplex.

If I knew more about noobs, creating the tar.xz, and scripting process I would make the Retropi/Kodi/Rasplex myself. With a baby due any day now i dont have much time to sit and read up on all of it.

I just watched your video on youtube and noticed you changed the theme in Rasplex, is this to make it so your script will show up? If there is any possible way to keep the default theme that would be awesome.