Questions regarding server encryption

I have just completed my ownCloud installation on a local Raspberry Pi 4. I would like to use it as Dropbox replacement mainly. The data is stored on a USB-(3.1)-attached SSD with 2TB.

I would like to ask if it would be safe to enable server-side encryption performance-wise on a Raspberry Pi 4? Will the hardware be capable of serving this, or will the cloud storage become unusable?

Also, I plan to set up regular and automated backups to my main NAS storage. When the files are encrypted by ownCloud, what else on top of the files themselves to I need to backup in order to be able to read those encrypted files again after a complete outage/loss of data?