PopOS is a solid choice. Other good choices are Mint or Zorin. But don't sweat it too much. Just pick something and go with it. Once you get into it more, you'll either know exactly what you want or you'll stop caring.
That applies to all Disney movies for me. The last one i saw was The Beauty and the Beast when it came out. My then girlfriend dragged me to the cinema to see it. It wasn't awful but I had no inclination to see another one ever since.
Retrieval. Indexing everything thoroughly is a bit of a faff but once you put in the work, finding that one invoice from two years ago becomes very easy. If that's not a factor for you, git will work too.
I'm wondering what all the Ethernet ports are good for in a home server setting? I have my box hooked up to the router but that's it. Seems like overkill to me.
Once you have some documents indexed, it'll learn to apply the correct metadata automatically. That works pretty well. You can also apply the data through the REST API, if you have the data available already. But yes, that's a bit of work. But paperless-ngx makes this easier than any other DMS I've ever used.
Paperless-ngx. It's a document management system for home users or small companies. Pretty cool if this is something you need. If you spend a lot of time filing away documents, you definitely need this.
Which would complete the handover of Iraq to Iran. Well done, Dubya.