Read: https://kodi.wiki/view/Internet_video_and_audio_streams
Create .strm files for each Soundcloud URL that you want to use as media. Kodi treats these like a media file with no metadata.
Create .nfo files for each .strm file. This is required. It also provides a way to add metadata, e.g. pretty names, if wanted.
Scrape the .nfo files to the Library.
Add Library items to a playlist.
Do something with the playlist, like script it being started 20 seconds after Kodi starts (how you do that is .. Google'able).
Plan B .. get a Raspberry Pi and use one of the many good niche distros or RPiOS installable apps/containers designed for "signage" use-cases, as that appears to be the end goal and something Kodi is not really designed for.