Power should be plenty and efficiency great. The only thing I wouldn‘t like is external HDDs.

Try Publii. It does everything for you. You can even set up the FTP upload.

+1

I‘ve been using a Hetzner Storage Box with Kopia via SFTP and was able to completely saturate my 500 Mbit/s upload.

Teacher here. No professional affiliation with PCs, Linux or self-hosting. Started out with a Synology NAS and got my first experiences with Linux, CLI, Docker, etc. Switched to Unraid last fall and I self-host quite a lot of services now. 100% self-taught.