No problem, friend.

Feel free to ask if you need some help setting stuff up and good luck!

Yes, end-to-end. Only you have access to the files. Proton does not.

Yes Sir.

I do a backup of Proxmox to the NAS once a week and auto-delete anything older than one month, and I upload those and all pictures and critical files to the cloud. Critical files being personal data, information about the house, insurance papers etc.
Personally I use Proton and have 1 TB, which has been more than enough. It is also encrypted.

Movies, music and TV shows are not backed up as I don’t consider them critical at all. It can all be re-downloaded if needed.

I know there is unRAID and TrueNAS, but I went with a traditional NAS (Synology, before all the fuckery) and a small N100 NUC on the side.
The NAS is critical for the whole family with backups, pictures and general files, so I need it to be 110%. On it, I just run the .arr stack, Surveilance Station and Qbit, and the NUC runs all my other containers like Jellyfin and Home Assistant. Full access to the files via NFS and it gives me good power for transcoding when needed. Even 4K high bitrate files play seamlessly on WiFi now.

It’s been rock solid and I would probably do it the same way again if I had to rebuild.

Best of luck finding the appropriate solution for your needs, mate!