Ok. I will. I forgot which version of Gapps is compatible with this ROM. I tried flashing ARM 6.0 Pico and ARM 7.1 Pico but they both failed. What version of Gapps are you using?
Gapps must be of the arm 7.1 version since this is a nougat release. You can use pico or any other level as long as they are 7.1
If you are coming from an android 6 rom i suggest you wipe everything and start over.
Use twrp 3.0.2.0 There are some later versions but i have read reports of where newer twrps are not working right and that might be why your attempted flashes are failing.
1) boot into twrp 3.0.2.0
2) BACKUP your current rom and data
3) Did I mention to BACKUP your current rom and data
4) Wipe .. ADVANCED wipe == Jumping from a Android 6 to Android 7 release you really need to wipe everything and start over
5) Flash the new rom
6) Flash superSU or magisk
7) Flash your gapps
8) Reboot --may take 5 to 8 minutes first time.