Starting bone stock unrooted, I followed op and successfully installed two after unlocking via fastboot. I flashed the new SuperSU and was on my way no issues. I did a backup of all but the data partitions (to keep the size of the backup down since permissions on twrp directory weren't able to be changed to allow me to copy the backup to my PC) . Today I tried to restore from that backup. The restore failed every time. The order was restoring boot, then system then system image, and Everytime it got halfways through the system step the phone would reboot and hang on the Google screen. After that happened the system partition couldn't be mounted in twrp seemingly having disappeared. I could not even mount it from the mount menu.I was finally able to remedy things thankfully as I was on my way to the zoo with my kids by u checking allow system to be mounted as read only and only selecting the system image option in restore, skipping the system step. That restore brought back my system image and allowed the phone to boot. I have no idea what happened but I'm scared to touch this thing again until I can either learn what I did wrong or until the bugs are worked out.
Does anyone have any insight to offer?