One thing you may want to explore is your OS. If you want to do what you suggested with a NAS OS like TrueNAS or Unraid. They can take advantage of a ssd cache. One small regular ssd for your OS, storage on your hdd array, and a NAS quality ssd that essentially runs your docker containers that gets backed up to your array.

It’s not nessesary. But if it’s something you think you might want to do in the future, you’ll want a plan for it now. Make sure you have enough mobo connections, and space in your case or an idea on how you would want to expand.