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NAS Hardware Configuration: best options for backup drives

I’m getting ready to purchase the hardware for setting up NAS at home. My question is about configuring the hard drives and chassis.

Personally, I’m more of a software/programming guy than a hardware guy. Hardware doesn’t come as naturally to me as software and programming languages.

I have three spheres-of-influence for which I desire the NAS.

Home. My spouse and I currently have files scattered all over various free cloud storage platforms and remembering which file is where and sharing and collaborating is getting tedious. Plus, we have 3 kids who will soon be needing network storage, so this will be places for them.
Media. I currently have >3TB of movies, plus music and photos fragmented on different physical hard drives and cloud space.
YouTube. I’m planning on launching a YouTube channel in the near-ish future, and I’ll have a lot of videos for that.
My thought was to get a 6-bay NAS chassis. HD1 for home storage with HD2 as backup. HD3 for media storage with HD4 as backup. HD5 for YouTube storage (eventually) with HD6 as backup.

Is that how this works? Is that how any of this works? When i finally purchase the hardware and start setting it up, can I configure synology or whatever to do that (A backs up to B, C backs up to D…)? Am I conceptualizing this all wrong, and should I be thinking about the hierarchy and architecture differently?