Don't over complicate this. Use a single container that runs the bot and can write to a host directory. Have the bot run yt-dlp whenever it finds a youtube link and download to the host directory. For moving the videos based on size you can write code in the bot to do it after download, or you can run a cron job to do it (either in the container or on the host), or maybe yt-dlp has an option for that.

I have a series of containers that use the host network and share messages over MQTT. Works well. One of them launches other containers when specific trigger phrases are said in specific topics. Another one sends trigger phrases based on a schedule.

Just use docker-compose? Put multiple containers in one compose file. Create an internal network for them to communicate with.

why not just use redis