Is your home connection down that much? I’d think that even syncing once every day or so would populate everything fine, and if you’re at home it should update over wifi.
I might just be spoiled because I’m the only one using mine and only for a handful of devices.
The second one.
Mirroring is good for speed, but a storage mechanism with parity checks will always be more recoverable. And you will have far more storage available.