That absolutely works, but when I built my offsite backup to hetzner I also thought about setting up own hardware and came to conclusion that for myself it doesn't really make a ton of sense. New RPi + 4TB ssd/m.2 drive with accessories adds up to something around 400€ (if that's even enough today), or few years worth of cloud backups. With own hardware there's always need to maintain it and hardware failures are always an option, so for me it makes more sense to just rely on big players with offsite backups. Your case might be different for various reasons, but sometimes renting capacity just makes more sense in the big picture.

I've been pleased with it. Family is very relaxed about projects like this, but yeah it's low power draw. I don't think I have anything special set up but the right thing to do for power would be to spin down drive when not in use, as power is dominated by the spinning rust.

Uptime is great. Only hiccups are that it can choke when compiling the ZFS kernel modules, triggered on kernel updates. It's an rpi 3/1GB RAM (I keep failing at forcing dkms to use only 1 thread, which would probably fix these hiccups 🤷).

That said, it is managed by me, so sometimes errors go unnoticed. I had recent issues where I missed a week of rsync because I switched from pihole to technitium on my home server and forgot to point the remote rpi there. This would all have been fixed with proper cron email setup...I'm clearly not a professional :)