I am hoping to have someone else with similar hardware to confirm High Sierra is running well on their iMac.
I have that same exact model iMac and HS is running fine on it. 8 GB is more than adequate.
The point is that people have all sorts of configurations. No two Macs remain the same after they leave the factory, but if you truly mean hardware compatibility, then you have no reason for concern.
If you are using Time Machine to back up to an Apple AirPort Time Capsule then you're all set. You can always restore your iMac from that backup.
Temporarily de-select "Back up automatically" to obviate the very unlikely possibility that upgrading to HS results in a Time Machine backup so enormous that it needs to reclaim all the Time Capsule's available space, leaving you with no Sierra system to restore.
Just be sure to re-select it eventually.