I've put together some wallpaper guidelines for my artistic distro a while ago, but the wiki with them is currently down. I'll post a link as soon as I get the wiki back. However, I'll probably have nothing to add, your draft seems perfect to me.
Regards -- Sergey "Shnatsel" Davidoff -- ubuntu-art mailing list ubuntu-art@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-art
