You seem on top of everything. No red flags when I look at what you are considering. Any will do great.

The Topnton i3-n305 Mini PC is a good choice. Intel NUC is another solid option, especially when used with a RAID enclosure for storage. Remember cooling is crucial for these devices, particularly if they’ll be housed in a small space. The importance of a good cooling solution cannot be overemphasized.

As for the operating system, Ubuntu is user-friendly and well-supported. You can run your desired applications like Plex or Jellyfin for media serving, qBittorrent, Sonarr, Radarr for torrenting, Wireguard for VPN, AdGuard or PiHole for ad-blocking, and Home Assistant for home automation, all on Linux. For managing these services, consider using Docker. It can help keep your system organized and simplify the process of updating. If you’re currently using them in a nas, you’re probably doing so already. But take the opportunity to clean things up, and if you’re not doing so already, use docker compose.

Foe backups, rsync can be used for local backups and Rclone for backing up to the cloud.